Remove leftover openstack code (#778)

There are still remnants of openstack in the Bandit code base.
Namely there was still a coverage step that relied on a openstack
git repo. Bandit is self contained and no longer only part of the
openstack ecosystem. Therefore it's safe to remove this coverage
step (which wasn't run anyway).

Signed-off-by: Eric Brown <browne@vmware.com>

tox.ini

@@ -56,13 +56,6 @@ commands =
     stestr run '{posargs}'
     coverage report
 
-[testenv:openstack_coverage]
-deps =
- -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt}
- PyYAML>=3.1.0
-       requests>=2.7.0
-commands = python tools/openstack_coverage.py
-
 [testenv:docs]
 deps = -r{toxinidir}/doc/requirements.txt
 commands=