Allow snapshots of paused and suspended instances

Change-Id: Id483d13d8d329aee4a57d0a89e6368fab3b201ec
Closes-Bug: #1256821
(cherry picked from commit 860b2a0be11ceb2e57c4c0d0e7ff020325277c78)
Merge branch 'stable/havana' of https://github.com/openstack/horizon into stable/havana_routerrules