Add a docs job to tox.ini

A noticed that there wasn't a docs option when running tox.
Thought it would be a good idea to add one.

Partial-Bug: #1331304
Change-Id: I5af9ff5d5986ad546146c0fa73eb98256fd00c5f

Author: Steve Martinelli

tox.ini

@@ -23,6 +23,10 @@ commands = python setup.py test --coverage --testr-args='{posargs}'
 [tox:jenkins]
 downloadcache = ~/cache/pip
 
+[testenv:docs]
+commands=
+    python setup.py build_sphinx
+
 [flake8]
 ignore = E126,E202,W602,H302,H402,E265,H305,H307,H405,H904
 show-source = True