Recent charmhelpers change forwards the broker requests to the
ceph-rbd-mirror with information about the RBD mirroring mode.
This is needed for Cinder Ceph Replication spec
Change-Id: I1d2b5351574a8741e55a8e6482d0c4a168562050
Co-authored-by: Ionut Balutiou <ibalutoiu@cloudbasesolutions.com>