Pflarr/fix autoexit

[Paul-Ferrell]

Code review checklist:

• Code is generally sensical and well commented
• Variable/function names all telegraph their purpose and contents
• Functions/classes have useful doc strings
• Function arguments are typed
• Added/modified unit tests to cover changes.
• New features have documentation added to the docs.
• New features and backwards compatibility breaks are noted in the RELEASE.md

[Paul-Ferrell]

This addresses an issue I found when doing PE testing this morning.
If you set autoexit to false, there's now a echo statement between the last command and the script end that will cause the test to pass even if it should have failed.
The other issues was that the err bash function should do an exit 1 rather than a return 1, so that script failure is forced even when autoexit is false.