Fail to rename ceph config file for cinder-backup

[Dai Dang Van]

### When I try to rename ceph.conf to ceph.abc.conf and reconfigure the Cinder services following:

backup_driver = cinder.backup.drivers.ceph.CephBackupDriver
backup_ceph_conf = /etc/ceph/ceph.abc.conf
backup_ceph_user = cinder-backup
backup_ceph_chunk_size = 134217728
backup_ceph_pool = backups

### I got this bug:

2019-01-02 18:14:13.059 8 ERROR oslo.service.loopingcall [-] Fixed interval looping call 'cinder.backup.manager.BackupManager._setup_backup_driver' failed: ObjectNotFound: [errno 2] error connecting to the cluster
2019-01-02 18:14:13.059 8 ERROR oslo.service.loopingcall Traceback (most recent call last):
2019-01-02 18:14:13.059 8 ERROR oslo.service.loopingcall File "/usr/lib/python2.7/site-packages/oslo_service/loopingcall.py", line 193, in _run_loop
2019-01-02 18:14:13.059 8 ERROR oslo.service.loopingcall result = func(*self.args, **self.kw)
2019-01-02 18:14:13.059 8 ERROR oslo.service.loopingcall File "/usr/lib/python2.7/site-packages/cinder/backup/manager.py", line 152, in _setup_backup_driver
2019-01-02 18:14:13.059 8 ERROR oslo.service.loopingcall backup_service.check_for_setup_error()
2019-01-02 18:14:13.059 8 ERROR oslo.service.loopingcall File "/usr/lib/python2.7/site-packages/cinder/backup/drivers/ceph.py", line 289, in check_for_setup_error
2019-01-02 18:14:13.059 8 ERROR oslo.service.loopingcall with rbd_driver.RADOSClient(self, self._ceph_backup_pool):
2019-01-02 18:14:13.059 8 ERROR oslo.service.loopingcall File "/usr/lib/python2.7/site-packages/cinder/volume/drivers/rbd.py", line 176, in __init__
2019-01-02 18:14:13.059 8 ERROR oslo.service.loopingcall self.cluster, self.ioctx = driver._connect_to_rados(pool)
2019-01-02 18:14:13.059 8 ERROR oslo.service.loopingcall File "/usr/lib/python2.7/site-packages/cinder/backup/drivers/ceph.py", line 298, in _connect_to_rados
2019-01-02 18:14:13.059 8 ERROR oslo.service.loopingcall client.connect()
2019-01-02 18:14:13.059 8 ERROR oslo.service.loopingcall File "/usr/lib/python2.7/site-packages/eventlet/tpool.py", line 186, in doit
2019-01-02 18:14:13.059 8 ERROR oslo.service.loopingcall result = proxy_call(self._autowrap, f, *args, **kwargs)
2019-01-02 18:14:13.059 8 ERROR oslo.service.loopingcall File "/usr/lib/python2.7/site-packages/eventlet/tpool.py", line 144, in proxy_call
2019-01-02 18:14:13.059 8 ERROR oslo.service.loopingcall rv = execute(f, *args, **kwargs)
2019-01-02 18:14:13.059 8 ERROR oslo.service.loopingcall File "/usr/lib/python2.7/site-packages/eventlet/tpool.py", line 125, in execute
2019-01-02 18:14:13.059 8 ERROR oslo.service.loopingcall six.reraise(c, e, tb)
2019-01-02 18:14:13.059 8 ERROR oslo.service.loopingcall File "/usr/lib/python2.7/site-packages/eventlet/tpool.py", line 83, in tworker
2019-01-02 18:14:13.059 8 ERROR oslo.service.loopingcall rv = meth(*args, **kwargs)
2019-01-02 18:14:13.059 8 ERROR oslo.service.loopingcall File "rados.pyx", line 875, in rados.Rados.connect (/builddir/build/BUILD/ceph-12.2.5/build/src/pybind/rados/pyrex/rados.c:9764)
2019-01-02 18:14:13.059 8 ERROR oslo.service.loopingcall ObjectNotFound: [errno 2] error connecting to the cluster
2019-01-02 18:14:13.059 8 ERROR oslo.service.loopingcall
2019-01-02 18:14:19.002 8 ERROR cinder.service [-] Manager for service cinder-backup compute16 is reporting problems, not sending heartbeat. Service will appear "down".
2019-01-02 18:14:29.003 8 ERROR cinder.service [-] Manager for service cinder-backup compute16 is reporting problems, not sending heartbeat. Service will appear "down".

### And the problem caused by missing clustername parameter for Rados object[1].

>>> cluster = rados.Rados(rados_id="cinder-backup", conffile='/etc/ceph/ceph.conf')
>>> cluster.connect()
>>> cluster.list_pools()
[u'volumes', u'images', u'backups', u'vms', u'journal_pool']
>>> cluster = rados.Rados(rados_id="cinder-backup", conffile='/etc/ceph/ceph.abc.conf')
>>> cluster.connect()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "rados.pyx", line 875, in rados.Rados.connect (/builddir/build/BUILD/ceph-12.2.5/build/src/pybind/rados/pyrex/rados.c:9764)
rados.ObjectNotFound: [errno 2] error connecting to the cluster
>>> cluster = rados.Rados(rados_id="cinder-backup", conffile='/etc/ceph/ceph.abc.conf', clustername="ceph")
>>> cluster.connect()
>>> cluster.list_pools()
[u'volumes', u'images', u'backups', u'vms', u'journal_pool']

I think we should have ceph_backup_cluster_name option as rbd driver already done[2].

[1] https://github.com/openstack/cinder/blob/master/cinder/backup/drivers/ceph.py#L294-L296
[2] https://github.com/openstack/cinder/blob/master/cinder/volume/drivers/rbd.py#L58