hammer.py: pg_hba.conf not found on rpm-based distros

https://jenkins.aws.isc.org/job/kea-dev/job/tarball-system-tests/92/execution/node/49/log/

00:08:02.790  |forge-srv1-f32-v4 14:27:28.880697| find: /etc/postgresql: No such file or directory
00:08:02.790  |forge-srv1-f32-v4 14:27:28.880704| sed: no input files