Besides implementing the required configuration entries in gnocchi.conf,
this commit also introduces code to create a symlink for the Python
rados library when the Ceph storage driver is chosen by the deployer.
Creation of Ceph Python library symlinks is usually done by the
ceph_client role. However, Gnocchi is different because it needs Ceph
access to be working when the DB sync task is run. Because the venv may
not exist before the os_gnocchi role runs, or because it might be
destroyed and recreated by the role, we need to create the symlink in
the os_gnocchi role itself.
Change-Id: I6b831867079bc24964c323e2784782d4eae30763
fb65850dbe