Added update-host for CGs in cinder-manage

Currently in cinder-manage, "update_host" command for consistency
groups is missing.

Hence, in a similar way like volumes and backups, 'update_host'
is added for Consistency Groups as well, because if host
configuration is changed then even if we change volumes and
backups using cinder-manage, we would have to go to the DB to
change our CGs.

Change-Id: I820ae9d17460a5aa7b3b2e41afc861e8bc0265a3
Closes-Bug: 1591153

cinder/cmd/manage.py

@@ -597,10 +597,33 @@ class ClusterCommands(BaseCommand):
             return 2
 
 
+class ConsistencyGroupCommands(object):
+    """Methods for managing consistency groups."""
+
+    @args('--currenthost', required=True, help='Existing CG host name')
+    @args('--newhost', required=True, help='New CG host name')
+    def update_cg_host(self, currenthost, newhost):
+        """Modify the host name associated with a Consistency Group.
+
+        Particularly to recover from cases where one has moved
+        a host from single backend to multi-backend, or changed the host
+        configuration option, or modified the backend_name in a multi-backend
+        config.
+        """
+
+        ctxt = context.get_admin_context()
+        groups = objects.ConsistencyGroupList.get_all(
+            ctxt, {'host': currenthost})
+        for gr in groups:
+            gr.host = newhost
+            gr.save()
+
+
 CATEGORIES = {
     'backup': BackupCommands,
     'config': ConfigCommands,
     'cluster': ClusterCommands,
+    'cg': ConsistencyGroupCommands,
     'db': DbCommands,
     'host': HostCommands,
     'logs': GetLogCommands,