Allow multiple clusters on RedHat

[gclough]

Currently RedHat is limited to a single cluster, by overriding the {{ postgresql_cluster_name }} with data. This was done to work within the SELinux restrictions, but my testing shows that you can use:

/var/lib/pgsql/{{ postgresql_version }}/{{ postgresql_cluster_name }}/data

If we use this structure, then the current SELinux config can stay, but we can have multiple clusters if we want.