update sphinx

Update sphinx to the version used to build the documentation elsewhere
and turn on the option to treat warnings as errors to ensure that no
poorly constructed rst is introduced. Cap sphinx<1.6.1, since that
version has a conflict with pbr right now.

Change-Id: I19b3332229e2094988cbf8968c42a0323194a209
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

setup.cfg

@@ -15,6 +15,7 @@ classifier =
 all_files = 1
 build-dir = doc/build
 source-dir = doc/source
+warning-is-error = 1
 
 [pbr]
 warnerrors = True

tox.ini

@@ -37,8 +37,8 @@ commands = bash -c "find {toxinidir}             \
 deps =
    Pygments
    docutils
-   sphinx>=1.1.2,<1.2
-   pbr>=0.6,!=0.7,<1.0
+   sphinx>=1.5.1,<1.6.1
+   pbr>=2.0.0,!=2.1.0
    oslosphinx
    nwdiag
    blockdiag
@@ -52,8 +52,8 @@ commands =
 
 [testenv:venv]
 deps =
-   pbr>=0.6,!=0.7,<1.0
-   sphinx>=1.1.2,<1.2
+   pbr>=2.0.0,!=2.1.0
+   sphinx>=1.5.1,<1.6.1
    oslosphinx
    blockdiag
    sphinxcontrib-blockdiag