FIX: dry run issues with config mode check

[ZLLentz]

Description

• Skip the "CONFIG" mode check when running in dry run mode
• Add a checkbox to the pre-merge checklist for verifying the script still works in dry_run mode

Motivation and Context

• dry_run runs no code on the target plc
• therefore, dry_run skips running the config mode check
• therefore, the assert always fails and you cannot run in dry_mode at all
• so, we use the built-in ansible_check_mode variable to bypass the assert for use in dry_run mode
• also add a checklist item so next time I remember to test using dry_run

How Has This Been Tested?

Interactively.
Before PR, dry_run script:

PLAY [plc-tst-bsd2] **************************************************************************************************************************************************************************************************************************************************************************

TASK [Gathering Facts] ***********************************************************************************************************************************************************************************************************************************************************************
ok: [plc-tst-bsd2]

TASK [Verify connectivity with ping] *********************************************************************************************************************************************************************************************************************************************************
ok: [plc-tst-bsd2]

TASK [Run PLC mode command] ******************************************************************************************************************************************************************************************************************************************************************
skipping: [plc-tst-bsd2]

TASK [Assert that PLC is in CONFIG mode] *****************************************************************************************************************************************************************************************************************************************************
fatal: [plc-tst-bsd2]: FAILED! => {"assertion": false, "changed": false, "evaluated_to": false, "msg": "PLC is in RUN mode! Abort!"}

After PR, dry_run script:

PLAY [plc-tst-bsd2] **************************************************************************************************************************************************************************************************************************************************************************

TASK [Gathering Facts] ***********************************************************************************************************************************************************************************************************************************************************************
ok: [plc-tst-bsd2]

TASK [Verify connectivity with ping] *********************************************************************************************************************************************************************************************************************************************************
ok: [plc-tst-bsd2]

TASK [Run PLC mode command] ******************************************************************************************************************************************************************************************************************************************************************
skipping: [plc-tst-bsd2]

TASK [Assert that PLC is in CONFIG mode] *****************************************************************************************************************************************************************************************************************************************************
skipping: [plc-tst-bsd2]

After PR, provision script (plc is in config):

TASK [Gathering Facts] ***********************************************************************************************************************************************************************************************************************************************************************
ok: [plc-tst-bsd2]

TASK [Verify connectivity with ping] *********************************************************************************************************************************************************************************************************************************************************
ok: [plc-tst-bsd2]

TASK [Run PLC mode command] ******************************************************************************************************************************************************************************************************************************************************************
ok: [plc-tst-bsd2]

TASK [Assert that PLC is in CONFIG mode] *****************************************************************************************************************************************************************************************************************************************************
ok: [plc-tst-bsd2]

After PR, provision script (plc is in run):

TASK [Gathering Facts] ***********************************************************************************************************************************************************************************************************************************************************************
ok: [plc-tst-bsd2]

TASK [Verify connectivity with ping] *********************************************************************************************************************************************************************************************************************************************************
ok: [plc-tst-bsd2]

TASK [Run PLC mode command] ******************************************************************************************************************************************************************************************************************************************************************
ok: [plc-tst-bsd2]

TASK [Assert that PLC is in CONFIG mode] *****************************************************************************************************************************************************************************************************************************************************
fatal: [plc-tst-bsd2]: FAILED! => {"assertion": false, "changed": false, "evaluated_to": false, "msg": "PLC is in RUN mode! Abort!"}

Where Has This Been Documented?

Added notes about implementing tasks for dry run mode at the bottom of https://confluence.slac.stanford.edu/display/PCDS/TcBSD+Ansible+Workflows

Pre-merge checklist

• Code works interactively
• Code contains descriptive docstrings, including context and API
• Pre-commit passes on GitHub Actions
• Documentation under https://confluence.slac.stanford.edu/display/PCDS/TcBSD has been updated appropriately

[ZLLentz]

One more thing to decide before review: I just remembered that you can also force a task to run even in check/dry_run mode. Maybe it's prudent to just always run the config mode check, and even skip the dry run if we're in run mode? Or maybe it's helpful to be able to run dry_run on a running PLC?

[ZLLentz]

After lunchtime pondering I think being able to dry_run on a prod PLC is a good thing, so I think as-implemented is correct.

[nrwslac]

Looks like ansible_check_mode is set internally by Ansible. The task then will only run when this flag is false. lgtm