[CI] shellcheck CI step and various shell fixes

[johnbley]

• Use set -e for almost all shell scripts (one exception which is commented)
• Pass shellcheck --severity=error
• Add CI step to run shellcheck

[johnbley]

Blergh. Apparently there is some combination of (a) things that lack of set -e was masking which were failing before, and (b) things where I should have been more careful applying set -e and that are expected to fail. Will dig deeper when I have more time.

[johnbley]

I'm going to close this and hopefully come back to do it piecewise (file-/directory- at a time). It certainly seems like a scheduled daily "full CI" might help with reducing bitrot/churn here as some of these tasks don't seem to have been run for weeks/months.

[marcalff]

I'm going to close this and hopefully come back to do it piecewise (file-/directory- at a time). It certainly seems like a scheduled daily "full CI" might help with reducing bitrot/churn here as some of these tasks don't seem to have been run for weeks/months.

@johnbley

Thanks.

This repository indeed has a lot of bitrot, no idea what was wrong with the failing tests earlier.