volume list: don't fail when there's no compute service

There may be deployments that only have a volume service but no compute
service, possibly as an intermediate step during the initial setup.
Don't fail the "volume list" command when no compute client can be
initiated.

Signed-off-by: Dr. Jens Harbott <harbott@osism.tech>
Change-Id: Idef77bdc8753a456a4c431b0385318dff6581a65

Author: osfrickler

openstackclient/volume/v2/volume.py

@@ -361,7 +361,6 @@ def get_parser(self, prog_name):
     def take_action(self, parsed_args):
 
         volume_client = self.app.client_manager.volume
-        compute_client = self.app.client_manager.compute
         identity_client = self.app.client_manager.identity
 
         if parsed_args.long:
@@ -393,6 +392,7 @@ def take_action(self, parsed_args):
         # Cache the server list
         server_cache = {}
         try:
+            compute_client = self.app.client_manager.compute
             for s in compute_client.servers.list():
                 server_cache[s.id] = s
         except Exception: