Enable DeprecationWarning in test environments
Enable DeprecationWarning in test environments

Many deprecations are triggered early (on imports, for example).
To make sure all DeprecationWarning messages are emitted we enable
them via the PYTHONWARNINGS environment variable.

Change-Id: Ib71e90531ebf6fae51f508c1c903c3fe346a93a7

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