MAINT: don't mess with plc ssh key configs, avoid Administrator account

[ZLLentz]

SSH Keys

While working on pcdshub/twincat-bsd-ansible#14 I realized that having the publickey option in the ssh config here means that:

• When logging into a plc, you can be first prompted to unlock your public key
• Your public key doesn't work anyway- we're not going around adding personal keys to every plc

Procedurally, doing it like this (after the edit) requires you to have access to the admin password, which seems in line with the procedure we want people to use for other protected systems like the switches etc.

Alternatively, we could do plc auth by having everyone send their public key to every plc, but that feels wrong.

Non-admin user

The other change here is to make it so you log in as a non-admin user by default. This means you need to opt-in as the Administrator user by doing e.g. ssh Administrator@plc-tst-bsd2, and if you simply ssh plc-tst-bsd2 you will log in as ecs-user instead.

[ZLLentz]

I plan to ask for reviewers on this first thing Monday morning.

[nrwslac]

lgtm.