Update scenarios doc for Ceph RGW
Update scenarios doc for Ceph RGW

Ceph RGW only runs on scenario004 for now.

Change-Id: I0385dc29635caeb1e7dd8f262c90b8f416d80e35

openstack/tripleo-heat-templates,dprince/tripleo-heat-templates,dprince/tripleo-heat-templates,openstack/tripleo-heat-templates