neutron: Disable rdo-release repository

The rdo repository should be disabled once the appliance is created
to avoid unintended updates to the openstack packages which could
lead to conflicts with the installed neutron agents.

Change-Id: I89c8b56786d1f4b90a3db33f9d21edef63bae624
Signed-off-by: Moti Asayag <masayag@redhat.com>