Modify query on pg_hba_file_rules to check for errors in regression tests

Modify query on pg_hba_file_rules to check for errors in regression tests

The regression tests include a query to check the execution path of
pg_hba_file_rules, but it has never checked that a given cluster has
correct contents in pg_hba.conf.  This commit extends the query of
pg_hba_file_rules to report any errors if anything bad is found.  For
EXEC_BACKEND builds, any connection attempt would fail when loading
pg_hba.conf if any incorrect content is found when parsed, so a failure
would be detected before even running this query.  However, this can
become handy for clusters where pg_hba.conf can be reloaded, where new
connection attempts are not subject to a fresh loading of pg_hba.conf.

Author: Julien Rouhaud, based on an idea from me
Discussion: https://postgr.es/m/YkFhpydhyeNNo3Xl@paquier.xyz