tox: Keeping going with docs

Sphinx 1.8 introduced [1] the '--keep-going' argument which, as its name
suggests, keeps the build running when it encounters non-fatal errors.
This is exceptionally useful in avoiding a continuous edit-build loop
when undertaking large doc reworks where multiple errors may be
introduced.

[1] https://github.com/sphinx-doc/sphinx/commit/e3483e9b045

Change-Id: I18032bd40489c4b1c511713b0f1c5bb1aca7c1d2

doc/requirements.txt

@@ -1,7 +1,9 @@
 # The order of packages is significant, because pip processes them in the order
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
-sphinx>=1.6.5,!=1.6.6,!=1.6.7,!=2.1.0;python_version>='3.4' # BSD
+
+sphinx>=1.8.0,<2.0.0;python_version=='2.7' # BSD
+sphinx>=1.8.0,!=2.1.0;python_version>='3.4' # BSD
 sphinxcontrib-apidoc>=0.2.0  # BSD
 openstackdocstheme>=1.20.0 # Apache-2.0
 reno>=2.5.0 # Apache-2.0

lower-constraints.txt

@@ -108,7 +108,7 @@ Routes==2.4.1
 setuptools==21.0.0
 simplejson==3.13.2
 snowballstemmer==1.2.1
-Sphinx==1.6.2
+Sphinx==1.8.0
 sphinxcontrib-websupport==1.0.1
 stestr==2.0.0
 stevedore==1.28.0

tox.ini

@@ -60,7 +60,7 @@ deps = -r{toxinidir}/doc/requirements.txt
 whitelist_externals = rm
 commands =
   rm -rf doc/build/
-  sphinx-build -b html doc/source doc/build/html
+  sphinx-build --keep-going -b html doc/source doc/build/html
 
 
 [testenv:pep8]
@@ -86,7 +86,7 @@ deps = -r{toxinidir}/doc/requirements.txt
 whitelist_externals = rm
 commands =
   rm -rf releasenotes/build
-  sphinx-build -a -E -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
+  sphinx-build -a -E -d releasenotes/build/doctrees --keep-going -b html releasenotes/source releasenotes/build/html
 
 [testenv:lower-constraints]
 deps =