Update docs building

Switch from python setup.py to calling sphinx-build directly, add
a new doc requirements.txt file.

Change-Id: I199b8ceff5740c775804ff0db52704df8cbd7b86

doc/requirements.txt

@@ -0,0 +1 @@
+zuul-sphinx>=0.2.0

setup.cfg

@@ -13,9 +13,3 @@ classifier =
     License :: OSI Approved :: Apache Software License
     Operating System :: POSIX :: Linux
     Programming Language :: Python
-
-[build_sphinx]
-all-files = 1
-warning-is-error = 1
-source-dir = doc/source
-build-dir = doc/build

test-requirements.txt

@@ -8,4 +8,3 @@ zuul
 ansible>=2.7.0,<2.8
 ansible-lint<4
 bashate>=0.2
-zuul-sphinx>=0.2.0

tox.ini

@@ -17,7 +17,10 @@ deps = bindep
 commands = bindep test
 
 [testenv:docs]
-commands = python setup.py build_sphinx
+deps =
+  -r{toxinidir}/doc/requirements.txt
+commands =
+  sphinx-build -W -b html -d doc/build/doctrees doc/source doc/build/html
 
 [testenv:linters]
 whitelist_externals = bash