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: Ief136815d6a0e1dfa0b8d1ffb42500fef38e39fe

lower-constraints.txt

@@ -36,7 +36,7 @@ requests==2.14.2
 restructuredtext-lint==1.1.1
 six==1.10.0
 snowballstemmer==1.2.1
-Sphinx==1.6.5
+Sphinx==1.8.0
 sphinxcontrib-websupport==1.0.1
 stevedore==1.20.0
 stestr==2.0.0

requirements.txt

@@ -6,7 +6,7 @@ pbr!=2.1.0,>=2.0.0 # Apache-2.0
 iso8601>=0.1.11 # MIT
 lxml!=3.7.0,>=3.4.1 # BSD
 docutils>=0.11 # OSI-Approved Open Source, Public Domain
-sphinx>=1.6.5,!=1.6.6,!=1.6.7,<2.0.0;python_version=='2.7'  # BSD
-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
 demjson>=2.2.2 # GLGPLv3+
 PyYAML>=3.12 # MIT

tox.ini

@@ -28,7 +28,8 @@ commands =
 
 [testenv:releasenotes]
 basepython = python3
-commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
+commands =
+  sphinx-build -a -E -W -d releasenotes/build/doctrees --keep-going -b html releasenotes/source releasenotes/build/html
 
 [testenv:sitemap]
 # commands = functional test command goes here
@@ -40,7 +41,7 @@ commands = {posargs}
 [testenv:docs]
 basepython = python3
 commands =
-  sphinx-build -W -b html -d doc/build/doctrees doc/source doc/build/html
+  sphinx-build -W --keep-going -b html -d doc/build/doctrees doc/source doc/build/html
 
 [testenv:bindep]
 # Do not install any requirements. We want this to be fast and work even if