add region to mistral_client

I originally wanted to add version and region to
all drivers, but I found that some drivers do not
have a version parameter, so I can only add it
after testing.


Change-Id: I675e3378fef903381e1dfe9bb55b096035a035db

vitrage/os_clients.py

@@ -194,6 +194,7 @@ def mistral_client():
     try:
         mi_client = driver_module('mistral')
         client = mi_client.Client(
+            region_name=CONF.service_credentials.region_name,
             session=keystone_client.get_session(),
         )
         LOG.info('Mistral client created')