Add doc8 to tox environment docs

Check reStructuredText documents for common style issues.

Change-Id: I10e61742e86d2d4781c5a00532c8e17d38a7d4b4

HACKING.rst

@@ -1,4 +1,4 @@
- Style Commandments
-===============================================
+Style Commandments
+==================
 
-Read the OpenStack Style Commandments http://docs.openstack.org/developer/hacking/
+Read the OpenStack Style Commandments http://docs.openstack.org/developer/hacking/

doc/source/usage.rst

@@ -5,7 +5,7 @@ Usage
 To use oslo.db in a project::
 
 * Session Handling
-  
+
   .. code:: python
 
     from oslo.config import cfg
@@ -32,7 +32,7 @@ To use oslo.db in a project::
 
   .. code:: python
 
-	from oslo.db import models
+    from oslo.db import models
 
 
     class ProjectSomething(models.TimestampMixin,
@@ -41,7 +41,7 @@ To use oslo.db in a project::
         ...
 
 
-* DB API backend support 
+* DB API backend support
 
   .. code:: python
 

test-requirements.txt

@@ -2,6 +2,7 @@ hacking>=0.9.2,<0.10
 
 coverage>=3.6
 discover
+doc8
 fixtures>=0.3.14
 MySQL-python
 psycopg2

tox.ini

@@ -35,6 +35,7 @@ commands = python setup.py testr --coverage --testr-args='{posargs}'
 
 [testenv:docs]
 commands =
+    doc8 -e .rst CONTRIBUTING.rst HACKING.rst README.rst doc/source
     python setup.py build_sphinx
 
 [flake8]