Fix python35 job failures
Fix python35 job failures

- inspect.getargspec()` was deprecated in Python 3.0 and will be removed
  in 3.6 (ETA late 2016). From Python 3.5 it started throwing a deprecation
  warning which leds some tests failures.

Change-Id: Ic57fd8629031a1a7a3e72b36bff133faf67544db

StackStorm/python-mistralclient,openstack/python-mistralclient,StackStorm/python-mistralclient,openstack/python-mistralclient