Blacklist bandit 1.6.0 and cap Sphinx on Python2

There's a regression[0] in bandit 1.6.0 which causes bandit to stop
respecting excluded directories, and our tests throw a bunch of
violations. Blacklist this version, but allow newer versions as there is
already a pull request[1] to fix it, and I expect it will be included in
the next release.

Also fix the requirements job which was broken by
https://review.opendev.org/657890 adding a cap on Sphinx on Python 2.

[0] https://github.com/PyCQA/bandit/issues/488
[1] https://github.com/PyCQA/bandit/pull/489

Co-Authored-By: Jake Yip <jake.yip@unimelb.edu.au>

Task: 33401
Story: 2005740

Change-Id: I34dc36c5236debc42424073af2c2d2104e18179a
(cherry picked from commit 913636b6b1fdcdbcfed951ad1ca68a5f84f7b8e0)
(cherry picked from commit eec7184fbc2de00d30752f16160c9553bdd2df7d)

doc/requirements.txt

@@ -4,5 +4,6 @@
 openstackdocstheme>=1.18.1 # Apache-2.0
 osprofiler>=1.4.0 # Apache-2.0
 os-api-ref>=1.4.0 # Apache-2.0
-sphinx!=1.6.6,!=1.6.7,>=1.6.2 # BSD
+sphinx!=1.6.6,!=1.6.7,>=1.6.2;python_version>='3.4' # BSD
+sphinx!=1.6.6,!=1.6.7,>=1.6.2,<2.0.0;python_version=='2.7' # BSD
 reno>=2.5.0 # Apache-2.0

test-requirements.txt

@@ -5,7 +5,7 @@
 # Despite above warning added by global sync process, please use
 # ascii betical order.
 
-bandit>=1.1.0 # Apache-2.0
+bandit!=1.6.0,>=1.1.0 # Apache-2.0
 bashate>=0.5.1 # Apache-2.0
 coverage!=4.4,>=4.0 # Apache-2.0
 doc8>=0.6.0 # Apache-2.0
@@ -17,7 +17,8 @@ osprofiler>=1.4.0 # Apache-2.0
 os-testr>=1.0.0 # Apache-2.0
 python-subunit>=1.0.0 # Apache-2.0/BSD
 pytz>=2013.6 # MIT
-sphinx!=1.6.6,!=1.6.7,>=1.6.2 # BSD
+sphinx!=1.6.6,!=1.6.7,>=1.6.2;python_version>='3.4' # BSD
+sphinx!=1.6.6,!=1.6.7,>=1.6.2,<2.0.0;python_version=='2.7' # BSD
 testrepository>=0.0.18 # Apache-2.0/BSD
 stestr>=2.0.0 # Apache-2.0
 testscenarios>=0.4 # Apache-2.0/BSD