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: Idf36ca3214dabc899cfdc7e5af20f29b8b86f4c3

requirements.txt

@@ -1,6 +1,10 @@
+# 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.
+
 pbr>=2.0.0,!=2.1.0 # Apache-2.0
-sphinx!=1.6.6,!=1.6.7,>=1.6.5,<2.0.0;python_version=='2.7' # BSD
-sphinx!=1.6.6,!=1.6.7,>=1.6.5,!=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
 testtools>=1.4.0
 yasfb>=0.8.0
 openstackdocstheme>=1.19.0 # Apache-2.0

tox.ini

@@ -12,8 +12,8 @@ deps = -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/
        -r{toxinidir}/test-requirements.txt
 whitelist_externals = find
 commands =
-    find . -type f -name "*.pyc" -delete
-    stestr run --slowest {posargs}
+  find . -type f -name "*.pyc" -delete
+  stestr run --slowest {posargs}
 
 [testenv:venv]
 basepython = python3
@@ -26,8 +26,8 @@ deps =
   -r{toxinidir}/requirements.txt
 setenv = PYTHONHASHSEED=0
 commands =
-    find . -type f -name "*.pyc" -delete
-    python setup.py build_sphinx
+  find . -type f -name "*.pyc" -delete
+  python setup.py build_sphinx
 
 [testenv:pdf-docs]
 basepython = python3
@@ -38,7 +38,7 @@ whitelist_externals =
   make
 commands =
   rm -rf doc/build/pdf
-  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:pep8]