Add a debug env for tox

Running a test with the pdb debugger was difficult because
tox captures output and causes the pdb prompt to quit.

Tips for how to run with debug are provided here:
https://wiki.openstack.org/wiki/Testr#Debugging_.28pdb.29_Tests

This change puts these commands into a debug env in tox.ini so
you can do a command like

tox -e debug

and when it hits your breakpoint you'll get the debug prompt.

Change-Id: I84b2df606db17209706d12f6f6a03e7812210d53

test-requirements.txt

@@ -2,6 +2,7 @@ hacking>=0.5.6,<0.8
 coverage>=3.6
 discover
 fixtures>=0.3.14
+oslotest>=1.2.0 # Apache-2.0
 python-subunit
 sphinx>=1.1.2
 testrepository>=0.0.17

tox.ini

@@ -24,6 +24,9 @@ commands = python setup.py testr --coverage --testr-args='{posargs}'
 [testenv:docs]
 commands = python setup.py build_sphinx
 
+[testenv:debug]
+commands = oslo_debug_helper -t translator/tests {posargs}
+
 [flake8]
 # H803 skipped on purpose per list discussion.
 # E123, E125 skipped as they are invalid PEP-8.