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: I1e3c52de2d0923902d75e850593de320f65612cd

doc/requirements.txt

@@ -1,4 +1,4 @@
-sphinx!=1.6.6,!=1.6.7,>=1.6.2;python_version>='3.4'  # BSD
+sphinx>=1.8.0,!=2.1.0;python_version>='3.4' # BSD
 sphinxcontrib-apidoc>=0.2.0  # BSD
 openstackdocstheme>=1.18.1 # Apache-2.0
 

lower-constraints.txt

@@ -50,7 +50,7 @@ requests==2.18.4
 rfc3986==1.1.0
 six==1.10.0
 snowballstemmer==1.2.1
-Sphinx==1.6.2
+Sphinx==1.8.0
 sphinxcontrib-websupport==1.0.1
 stevedore==1.28.0
 stestr==2.0.0

tox.ini

@@ -28,7 +28,7 @@ commands = stestr run {posargs}
 
 [testenv:docs]
 deps = -r{toxinidir}/doc/requirements.txt
-commands = sphinx-build -W -b html doc/source doc/build/html
+commands = sphinx-build -W --keep-going -b html doc/source doc/build/html
 
 [testenv:pdf-docs]
 envdir = {toxworkdir}/docs
@@ -36,12 +36,12 @@ deps = {[testenv:docs]deps}
 whitelist_externals =
   make
 commands =
-  sphinx-build -W -b latex doc/source doc/build/pdf
+  sphinx-build -W --keep-going -b latex doc/source doc/build/pdf
   make -C doc/build/pdf
 
 [testenv:releasenotes]
 deps = {[testenv:docs]deps}
-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
 
 [hacking]
 import_exceptions = congressclient.i18n