Reduce error handling verbosity in CI tests scripts

[AjayThorve]

This PR adds a less verbose trap method, for error handling to help ensure that we capture all potential error codes in our test scripts, and works as follows:

• setting an environment variable, EXITCODE, with a default value of 0
• setting a trap statement triggered by ERR signals which will set EXITCODE=1 when any commands return a non-zero exit code

cc @ajschmidt8

[ajschmidt8]

/merge

[bdice]

Great. This is the solution I had in mind.