Report test_atomic_ops() failures consistently, via macros.

This prints the unexpected value in more failure cases, and it removes
forty-eight hand-maintained error messages.  Back-patch to 9.5, which
introduced these tests.

Reviewed (in an earlier version) by Andres Freund.

Discussion: https://postgr.es/m/20190915160021.GA24376@alvherre.pgsql