Reduce number of novaclient calls

Currently, each client creates a new session for
each call. This fix makes novaclient re-use
sessions in the most obvoius cases.

Conflicts:
	openstack_dashboard/api/nova.py

Partial-Bug: #1247056

Change-Id: Ie99ecb66304cf40e4f5fdd31fab5162ed11b863e
(cherry picked from commit ddc479272f)

openstack_dashboard/api/nova.py

@@ -670,8 +670,9 @@ def service_list(request):
 
 def aggregate_list(request):
     result = []
-    for aggregate in novaclient(request).aggregates.list():
-        result.append(novaclient(request).aggregates.get_details(aggregate.id))
+    c = novaclient(request)
+    for aggregate in c.aggregates.list():
+        result.append(c.aggregates.get_details(aggregate.id))
 
     return result