refactor: set errexit pragma

[MitchellPaff]

Failure (when running locally with set -x):

Warning: Could not find base configuration, try setting the BDECOPY_DATADIR env variable to a directory containing a file with the same base name as the executable and the .cfg extension

[kodiakhq]

This PR currently has a merge conflict. Please resolve this and then re-add the automerge label.

[l0b0]

Failure investigation:

1. The error happens on the "$exe" -c ../test5.cfg ../par1.crs par5a.out par5a.log line.
2. bde_copy returns 1 when running that line, with an error message "Cannot open metadata file ../par1.crs.hdr".
3. The previous line, "$exe" -c ../test4.cfg ../par1.crs par4.out par4.log, succeeded. The only difference between the two lines is the output files and the .cfg files. The only difference between the .cfg files is that test5.cfg has a metadata_extension .hdr line, which looks like it's relevant.
4. The metadata_extension .hdr line has always been in that .cfg file.

I'll need to do a quick bisect applying this change at every step to figure out when this started failing, but for now I assume it's been failing forever, since there's no direct validation of the result of every single command.