The Ceph relation adapter and keyring helper code was moved to
``charms.openstack`` as part of development of the
``ceph-rbd-mirror`` charm.

Port the Gnocchi charm to re-use this code.

Depends-On: If1d645f4708e27b724f93cac0e14431137c885d7
Depends-On: I97b4c30dabfcf65ec3fb876c2a09a44172be85e7
Change-Id: If0da7f1efcfa6b61aa210edcd76e9c3392e0e8e9