purge: stop rgw instances by iteration

purge: stop rgw instances by iteration

It looks like that the service module doesn't support wildcard anymore
for stopping/disabling multiple services.

fatal: [rgw0]: FAILED! => changed=false
  msg: 'This module does not currently support using glob patterns,
        found ''*'' in service name: ceph-radosgw@*'
...ignoring

Instead we should iterate over the rgw_instances list.

Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>
(cherry picked from commit 9d3b49293d785b9b2b6bb902bce0ae8bce6b4e6e)