setup ceph-mgr daemon for luminous rc and greater
setup ceph-mgr daemon for luminous rc and greater

ceph-mgr daemon is required as part of Ceph cluster from
luminous release onwards.

Change-Id: I0903b3cd9fa84041bcd7ed5034d8a60d14759e92
Closes-Bug: #1708169

ajarr/devstack-plugin-ceph,openstack/devstack-plugin-ceph