Make volume snapshots_client to use **kwargs

As we discussed on
http://lists.openstack.org/pipermail/openstack-dev/2015-July/068864.html
All http POST/PUT methods need to contain **kwargs as their arguments.

This patch makes volume snapshots_client use **kwargs.

Partially implements blueprint consistent-service-method-names

Change-Id: I1fc18a879702a2f77ebbe704fa2e9c5eaa96b220
diff --git a/tempest/api/compute/volumes/test_volume_snapshots.py b/tempest/api/compute/volumes/test_volume_snapshots.py
index a00c0ba..f42d153 100644
--- a/tempest/api/compute/volumes/test_volume_snapshots.py
+++ b/tempest/api/compute/volumes/test_volume_snapshots.py
@@ -50,7 +50,7 @@
         s_name = data_utils.rand_name('Snapshot')
         # Create snapshot
         snapshot = self.snapshots_client.create_snapshot(
-            volume['id'],
+            volume_id=volume['id'],
             display_name=s_name)['snapshot']
 
         def delete_snapshot(snapshot_id):