Add debug to tox enviroment

We can simply run `tox -e debug <test_name>` to debug test.

Change-Id: Ibb46d95eb44f929b27cec672095cf0c70dcfa9d8

tox.ini

@@ -14,6 +14,7 @@ deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 commands = bash tools/pretty_tox.sh '{posargs}'
 whitelist_externals = bash
+                      find
 
 [testenv:py27-mitaka]
 install_command = pip install -chttps://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt?h=stable/mitaka {opts} {packages}
@@ -31,6 +32,11 @@ commands = {posargs}
 [testenv:cover]
 commands = {toxinidir}/tools/cover.sh {posargs}
 
+[testenv:debug]
+commands =
+  find . -type f -name "*.pyc" -delete
+  oslo_debug_helper {posargs}
+
 [testenv:docs]
 commands = python setup.py build_sphinx