Fix python3 compatibility of rbd get_fsid

In py3 librados's get_fsid() function returns a binary string
which breaks comparison when compared with the same value as a
string. This is currently breakin the logic that compares ceph
cluster fsids when deciding whether the image used to boot an
instance is cow-clonable.

Change-Id: I79b40ca40400c67b0805926096317afd875ffabb
Closes-Bug: #1816468
(cherry picked from commit e8b6b0bc78)
(cherry picked from commit b4b47a59c7)

nova/tests/unit/virt/libvirt/storage/test_rbd.py

@@ -119,6 +119,13 @@ class RbdTestCase(test.NoDBTestCase):
             self.assertFalse(self.driver.is_cloneable({'url': loc},
                                                       image_meta))
 
+    @mock.patch.object(rbd_utils, 'RADOSClient')
+    def test_rbddriver(self, mock_client):
+        client = mock_client.return_value
+        client.__enter__.return_value = client
+        client.cluster.get_fsid.side_effect = lambda: b'abc'
+        self.assertEqual('abc', self.driver.get_fsid())
+
     @mock.patch.object(rbd_utils.RBDDriver, 'get_fsid')
     def test_cloneable(self, mock_get_fsid):
         mock_get_fsid.return_value = 'abc'

nova/virt/libvirt/storage/rbd_utils.py

@@ -28,6 +28,7 @@ from oslo_concurrency import processutils
 from oslo_log import log as logging
 from oslo_serialization import jsonutils
 from oslo_service import loopingcall
+from oslo_utils import encodeutils
 from oslo_utils import excutils
 from oslo_utils import units
 
@@ -194,7 +195,7 @@ class RBDDriver(object):
 
     def get_fsid(self):
         with RADOSClient(self) as client:
-            return client.cluster.get_fsid()
+            return encodeutils.safe_decode(client.cluster.get_fsid())
 
     def is_cloneable(self, image_location, image_meta):
         url = image_location['url']
@@ -204,6 +205,7 @@ class RBDDriver(object):
             LOG.debug('not cloneable: %s', e)
             return False
 
+        fsid = encodeutils.safe_decode(fsid)
         if self.get_fsid() != fsid:
             reason = '%s is in a different ceph cluster' % url
             LOG.debug(reason)