Require assisted_volume_snapshots from novaclient

The "QEMU-assisted-snapshots for GlusterFS volumes" patch currently
does a try/except ImportError for the new assisted_volume_snapshots
extension in novaclient.  That functionality is now in novaclient
2.15.0, so Cinder should consider this a hard requirement rather
than allowing it to be absent.

Change-Id: I5d5b4918f17f26706bed361cbbe8b369b10b0b98

cinder/compute/nova.py

@@ -20,10 +20,7 @@ Handles all requests to Nova.
 from novaclient import extension
 from novaclient import service_catalog
 from novaclient.v1_1 import client as nova_client
-try:
-    from novaclient.v1_1.contrib import assisted_volume_snapshots
-except ImportError:
-    assisted_volume_snapshots = None
+from novaclient.v1_1.contrib import assisted_volume_snapshots
 from oslo.config import cfg
 
 from cinder.db import base
@@ -100,9 +97,7 @@ def novaclient(context, admin=False):
 
     LOG.debug(_('Novaclient connection created using URL: %s') % url)
 
-    extensions = []
-    if assisted_volume_snapshots:
-        extensions.append(assisted_volume_snapshots)
+    extensions = [assisted_volume_snapshots]
 
     c = nova_client.Client(context.user_id,
                            context.auth_token,

requirements.txt

@@ -16,7 +16,7 @@ Paste
 PasteDeploy>=1.5.0
 python-glanceclient>=0.9.0
 python-keystoneclient>=0.3.0
-python-novaclient>=2.12.0
+python-novaclient>=2.15.0
 python-swiftclient>=1.5
 Routes>=1.12.3
 six