Improve and fix some issues in the TAP tests of pg_upgrade

Improve and fix some issues in the TAP tests of pg_upgrade

This is based on a set of suggestions from Noah, with the following
changes made:
- The set of databases created in the tests are now prefixed with
"regression" to not trigger any warnings with name restrictions when
compiling the code with -DENFORCE_REGRESSION_TEST_NAME_RESTRICTIONS, and
now only the first name checks after the Windows case of double quotes
mixed with backslashes.
- Fix an issue with EXTRA_REGRESS_OPTS, which were not processed in a
way consistent with 027_stream_regress.pl (missing space between the
option string and pg_regress).  This got introduced in 7dd3ee5.
- Add a check on the exit code of the pg_regress command, to catch
failures after running the regression tests.

Reviewed-by: Noah Misch
Discussion: https://postgr.es/m/YoHhWD5vQzb2mmiF@paquier.xyz