Support all common SHELLs

[mkandes]

The current version of galyleo is not compatible with all SHELLs. e.g., users of zsh on Expanse have recently reported problems with the new validation checks/tests now performed prior to submitting the galyleo job to the scheduler.

This will not be a simple issue to resolve. But it may be one of the first key issues that could motivate transitioning galyleo from (Ba)sh to Python in the future.