Add debug environment to tox

the debug environment is based on oslo_debug_helper and enables devs to
use pdb for debugging the client. [1]

[1] http://docs.openstack.org/developer/oslotest/features.html

Change-Id: I4b15a4abd8b3391f1ec87f55194757e798b18ba8

tox.ini

@@ -28,6 +28,12 @@ commands =
     coverage combine
     coverage report -m
 
+[testenv:debug]
+deps =
+    oslotest
+    {[testenv]deps}
+commands = oslo_debug_helper -t tripleoclient/tests {posargs}
+
 [testenv:docs]
 commands = python setup.py build_sphinx