Enable bandit in gate

Run security linter bandit as part of pep8. Pep8 is the usual
linter target and thus let's use it there instead of starting
another short-running job to enable it.

Change-Id: I8b5dc551b51ea5b92d755927d811f9b60e87e4d2

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 minversion = 1.6
-envlist = py34,py27,pep8,bandit
+envlist = py34,py27,pep8
 
 [testenv]
 deps = -r{toxinidir}/test-requirements.txt
@@ -10,7 +10,10 @@ commands =
   coverage report --show-missing
 
 [testenv:pep8]
-commands = flake8
+commands =
+  flake8
+  # Run security linter
+  bandit -r oslo_log -n5
 
 [testenv:venv]
 commands = {posargs}
@@ -24,7 +27,6 @@ commands =
   coverage report --show-missing
 
 [testenv:bandit]
-deps = -r{toxinidir}/test-requirements.txt
 commands = bandit -r oslo_log -n5
 
 [flake8]