Add `service_ensure`.

This allows you to control the status of the Postgresql service directly
from postgresql::server.
Update for RHEL7.

Block RHEL7 from pulling in the PostgreSQL repos from upstream as they
don't exist yet.
This doesn't exist on RHEL7.
Handle ports for systemd.

This is a terrible hack currently but it appropriately handles systemd.
Ensure repo is in place before postgis installation.

We need to make sure we've actually setup the repo before installing
postgis.
Ensure we've always started postgresql at least once before a reload.
Add the template for port overriding on RHEL7.

This lets us tell systemd to do the right thing.  Can be extended later
for PGDATA.
Various test updates to handle RHEL7 better.
Make sure we set selinux contexts on Redhat.
Make sure we continue working post 7.0.