Add doc8 checks to docs tox target.

And fix the one error that it throws up.

Change-Id: I51fb24562b5779fc40b9e8fcd3a62c5ea5478faf

doc/source/contents.rst

@@ -10,7 +10,8 @@ Documentation
 Summary
 -----------------
 
-`Cloud-init`_ is the *defacto* multi-distribution package that handles early initialization of a cloud instance.
+`Cloud-init`_ is the *defacto* multi-distribution package that handles
+early initialization of a cloud instance.
 
 .. toctree::
     :maxdepth: 2

test-requirements.txt

@@ -13,4 +13,5 @@ oslosphinx
 
 # For style checking
 hacking<0.11,>=0.10.0
+doc8
 coverage

tox.ini

@@ -25,7 +25,9 @@ commands = nosetests --with-coverage --cover-erase --cover-package=cloudinit --c
 commands = flake8 {posargs}
 
 [testenv:docs]
-commands = python setup.py build_sphinx
+commands =
+    python setup.py build_sphinx
+    doc8 doc/source
 
 [testenv:venv]
 commands = {posargs}