Ensure that configs exist before editing on Red Hat systems
Make sure that rpc_backend gets set in quantum.conf
Make sure the plugin.ini symbolic link gets set up
Fixup for RH not having separate OVS plugin/agent pkgs
Fix DHCP agent for RH which has no sep. pkg for it
Make sure that the openvswitch agent service really gets enabled
Make sure dhcp_agent.ini is installed prior to editing it

Redhat distros don't have a separate dhcp agent package, so we have to
make sure that the quantum package gets installed before editing
dhcp_agent.ini.
to make sure that the quantum package is installed before editing the
Fix previous DHCP fix