post-install commands are executed with bash -l so it's creating a new login shell

[ThaDaVos]

Describe the bug
A clear and concise description of what the bug is.

It seems the post-install commands are called with bash -l when using clr-installer --config ... in the live-server installer - this creates a new bash login shell, which in turns triggers .bash_login if it exists - I have a modified live-server image which has the .bash_login in the roots home directory, so it's getting called again, which isn't functional as the script it calls requires input from the user, so halting the post-install script without any means of interaction

To Reproduce
Steps to reproduce the behavior:

1. Create a custom live-iso which has a .bash_login inside the root home directory which requests users input
2. Use a config with a post-install command
3. call clr-installer with your config
4. See it hang indefinitely

Expected behavior
A clear and concise description of what you expected to happen.

I expected it to be called with just bash not bash -l, so to execute normally

Screenshots
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Environment (please complete the following information):

• Clear Linux OS Version: [swupd info] 42210
• Installer Version [clr-installer -v] 2.7.11
• Platform: [hardware infomation] N/A

Additional context
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