Use linters tox environment

Follow change I2afa7931bf3e18798b95a8af33ccf5ef761c4ad5 on
project-config and introduce a new linters target that is used
for linting on the repo.

Change-Id: I1f81b8ab1fe18a172804b795e40428034fddd803

tox.ini

 [tox]
 minversion = 1.6
-envlist = pep8,jjb,jenkins-project,zuul
+envlist = linters,jjb,jenkins-project,zuul
 skipsdist = True
 
 [testenv]
 deps = -r{toxinidir}/test-requirements.txt
 
+[testenv:linters]
+commands =
+  flake8
+  {toxinidir}/tools/run-bashate.sh
+
 [testenv:pep8]
 commands =
   flake8