Add back a bandit tox job

The bandit project uses an integration test to ensure it doesn't
break other projects by introducing new changes. To run this
integration, it is necessary to have a common tox target of 'bandit'

Change-Id: If44008f6a48134a8af38e6794fb87ae09aac57b4

tox.ini

@@ -21,6 +21,11 @@ commands =
   flake8
   bandit -c bandit.yaml -r keystoneclient -n5 -p gate
 
+[testenv:bandit]
+# NOTE(browne): This is required for the integration test job of the bandit
+# project. Please do not remove.
+commands = bandit -c bandit.yaml -r keystoneclient -n5 -p gate
+
 [testenv:venv]
 commands = {posargs}