Enable DeprecationWarning in test environments
Enable DeprecationWarning in test environments

Many deprecations are triggered early (on imports, for example)
before the warnings are enabled by the WarningsFixture in the
base test class.

To make sure all DeprecationWarning messages are emitted we enable
them via the PYTHONWARNINGS environment variable.

Change-Id: Idb12c1383d8cbf8b22eed7bd9877d6e4fbc8bcc8

openstack/dragonflow,openstack/dragonflow,openstack/dragonflow