tox: Keeping going with docs and cleanup setup.cfg

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. pbr hasn't need the hook configuration since forever [2]

[1] https://github.com/sphinx-doc/sphinx/commit/e3483e9b045
[2] c84876dc0f

Change-Id: I22e930f9876ca29750093a78e4bf3a7d4a479eb9

doc/requirements.txt

@@ -1,6 +1,7 @@
 # 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.
+
 openstackdocstheme>=1.18.1 # Apache-2.0
 reno>=2.5.0 # Apache-2.0
-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

setup.cfg

@@ -19,9 +19,6 @@ author = OpenStack
 author_email = openstack-discuss@lists.openstack.org
 home-page = https://launchpad.net/blazar
 
-[global]
-setup-hooks = pbr.hooks.setup_hook
-
 [files]
 packages =
     blazarclient

tox.ini

@@ -50,4 +50,4 @@ deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://opendev.org/openstack/requirements/raw/branch/master/upper-constraints.txt}
   -r{toxinidir}/requirements.txt
   -r{toxinidir}/doc/requirements.txt
-commands = sphinx-build -a -W -E -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
+commands = sphinx-build -a -W -E -d releasenotes/build/doctrees --keep-going -b html releasenotes/source releasenotes/build/html