[neutron] Avoid running neutron-db-manage twice
[neutron] Avoid running neutron-db-manage twice

- L3 Router service plugin will be always present into SERVICE_PLUGINS
  list, so packstack is running neutron-db-manage twice.

Change-Id: Ia1d8f14f85f1861e52d9359dd71b265e091ddb46
Signed-off-by: Gael Chamoulaud <68646863a1a9108d0246eb96cb6356f9fa9a34f3@redhat.com>

openstack/packstack,fr34k8/packstack,stackforge/packstack,fr34k8/packstack,imcsk8/packstack,mahak/packstack,stackforge/packstack,mahak/packstack,openstack/packstack,xbezdick/packstack,openstack/packstack,xbezdick/packstack,mahak/packstack,imcsk8/packstack,stackforge/packstack,fr34k8/packstack,xbezdick/packstack,imcsk8/packstack