charms capable of relating to ceph build the list of monitor hosts
from the ceph-public-address in the relation data or simply using the
private-address field provided by juju.
This patch populates ceph-public-address in the relations with the
list of monitor hosts provided in the configuration, so clients connect
directly to the non juju managed ceph and not to ceph-proxy IP.
Closes-Bug: #1642430
Change-Id: Ib2e3c6a8b0d9fc0b6d729d845a802945b64fc74c