Add debug testenv in tox

Once we add debug testenv, we can use "tox debug -- --debug"
to debug test cases when tox is running.

Change-Id: I6f56257e4bbe3f9e303c014f169f016c5668269e

test-requirements.txt

@@ -6,6 +6,7 @@ hacking<0.11,>=0.10.2
 mox>=0.5.3
 mock>=1.0
 oslo.sphinx
+oslotest>=1.10.0 # Apache-2.0
 pylint==0.25.2
 python-subunit>=0.0.18
 sphinx!=1.2.0,!=1.3b1,<1.3,>=1.1.2

tox.ini

@@ -26,6 +26,9 @@ sitepackages = False
 commands =
   flake8 {posargs}
 
+[testenv:debug]
+commands = oslo_debug_helper {posargs}
+
 [testenv:genconfig]
 commands = oslo-config-generator --config-file=etc/gceapi/gceapi-config-generator.conf