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: I3a7882781a6ccea75c6dc6c970cce6622a265716

openstack/networking-mlnx,openstack/networking-mlnx,stackforge/networking-mlnx,stackforge/networking-mlnx