Support CentOS in postgresql config.py path

[Pete MacKinnon]

The PGSQL_CONFIG and PSQL_HBA_CONFIG values need specific assignment for the 'redhat' family (CentOS, RHEL, Fedora). The locations of those conf files are defaulted to their normal location after a call to initdb (/var/lib/pgsql/data).

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/172228

[Pete MacKinnon (pmackinn)]

Comments in patch set 4 in https://review.openstack.org/#/c/147908/ applicable here.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/188912

[OpenStack Infra (hudson-openstack)]

Change abandoned by Alex Tomic (<email address hidden>) on branch: master
Review: https://review.openstack.org/188912
Reason: Abandoning as this functionality will be superceded by the config groups work on pgsql

[OpenStack Infra (hudson-openstack)]

Change abandoned by Nikhil Manchanda (<email address hidden>) on branch: master
Review: https://review.openstack.org/172228
Reason: Hi there! We're abandoning this change since there haven't been any updates in the last 60 days. Feel free to restore this change if it's still work in progress. Also do ping us on #openstack-trove so that we can help with the reviews. Thanks!