tests: Make postmaster/002_connection_limits deal verbose logs
When log_error_verbosity=verbose is configured the test would hand (and then
fail), because of the sqlstate being added between log level and message. Make
regex cope.
Reported-by: Andrew Dunstan <andrew@dunslane.net>
Discussion: https://postgr.es/m/
c7ba6bd0-3701-43d1-9087-
017777fe9cd2%40dunslane.net