Switch to current Sphinx

Update requirements to current Sphinx version. Don't auto-upgrade to
next major version.

Fix one lexing issue.

Change-Id: I6e4164661a8b21cc6251176afe8020df8a914011

doc/contributor-guide/source/project-deploy-guide.rst

@@ -85,7 +85,7 @@ does alter the standard linking conventions.
 
 Usage for the deploy guide is as follows:
 
-.. code-block:: ini
+.. code-block:: rst
 
    :deploy_guide:`Link title text <last-part-of-url.html>`
 

test-requirements.txt

@@ -9,7 +9,7 @@ hacking<0.12,>=0.11.0 # Apache-2.0
 beautifulsoup4 # MIT
 Jinja2>=2.8 # BSD License (3 clause)
 openstack-doc-tools>=1.1.0 # Apache-2.0
-sphinx!=1.3b1,<1.4,>=1.2.1 # BSD
+sphinx>=1.5.1,<1.6 # BSD
 openstackdocstheme>=1.5.0 # Apache-2.0
 doc8 # Apache-2.0
 requests>=2.10.0,!=2.12.2  # Apache-2.0
@@ -17,6 +17,5 @@ requestsexceptions>=1.1.1 # Apache-2.0
 sphinxmark
 lxml>=2.3,!=3.7.0  # BSD
 
-
 # For translations
 Babel>=2.3.4  # BSD