tox: Keeping going with docs

1. 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.

2. Remove the unnecessary blank line for tox.ini

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

Change-Id: Ie837d376bb1a1d93367369d25140dd8a9d5ac14e

sync/doc/requirements.txt

@@ -9,8 +9,8 @@
 # openstack-ansible-tests repository. Once it merges there, the changes will
 # automatically be proposed to all the repositories which use it.
 
-sphinx!=1.6.6,!=1.6.7,>=1.6.2,<2.0.0;python_version=='2.7'  # BSD
+sphinx>=1.8.0,<2.0.0;python_version=='2.7' # BSD
-sphinx>=1.8.0,!=2.1.0,>=1.6.2;python_version>='3.4'  # BSD
+sphinx>=1.8.0,!=2.1.0;python_version>='3.4'  # BSD
 sphinxcontrib-svg2pdfconverter>=0.1.0 # BSD
 openstackdocstheme>=1.20.0 # Apache-2.0
 reno>=2.5.0 # Apache-2.0

tox.ini

@@ -3,7 +3,6 @@ minversion = 2.0
 skipsdist = True
 envlist = docs,linters,func
 
-
 [testenv]
 usedevelop = True
 install_command =
@@ -26,35 +25,31 @@ setenv =
     VIRTUAL_ENV={envdir}
     WORKING_DIR={toxinidir}
 
-
 [testenv:docs]
 basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 commands =
     bash -c "rm -rf doc/build"
     doc8 doc
-    sphinx-build -b html doc/source doc/build/html
+    sphinx-build --keep-going -b html doc/source doc/build/html
 
 [testenv:pdf-docs]
 basepython = python3
 deps = {[testenv:docs]deps}
 whitelist_externals =
-  make
 commands =
-  sphinx-build -W -b latex doc/source doc/build/pdf
+  sphinx-build --keep-going -W -b latex doc/source doc/build/pdf
   make -C doc/build/pdf
 
 [doc8]
 # Settings for doc8:
 extensions = .rst
 
-
 [testenv:releasenotes]
 basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 commands =
-    sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
+    sphinx-build -a -E -W -d releasenotes/build/doctrees --keep-going -b html releasenotes/source releasenotes/build/html
-
 
 # environment used by the -infra templated docs job
 [testenv:venv]
@@ -62,43 +57,36 @@ basepython = python3
 commands =
     {posargs}
 
-
 [testenv:pep8]
 basepython = python3
 commands =
     bash -c "{toxinidir}/tests/common/test-pep8.sh"
 
-
 [flake8]
 # Ignores the following rules due to how ansible modules work in general
 #     F403 'from ansible.module_utils.basic import *' used;
 #          unable to detect undefined names
 ignore=F403
 
-
 [testenv:bashate]
 basepython = python3
 commands =
     bash -c "{toxinidir}/tests/common/test-bashate.sh"
 
-
 [testenv:ansible-syntax]
 basepython = python3
 commands =
     bash -c "{toxinidir}/tests/common/test-ansible-syntax.sh"
 
-
 [testenv:ansible-lint]
 basepython = python3
 commands =
     bash -c "{toxinidir}/tests/common/test-ansible-lint.sh"
 
-
 [testenv:functional]
 commands =
     bash -c "{toxinidir}/tests/common/test-ansible-functional.sh"
 
-
 [testenv:linters]
 basepython = python3
 commands =