Fix layout-checks.py to work in virtualenv

Fix the python interpreter used by layout-checks.py so that the "tox -e
zuul" target works correctly on a local system.

Add the PyYAML dependency needed by layout-checks.py to the tox
configuration for the zuul target.

Add the zuul target to the default list for tox.

Change-Id: Ic4db9fc3bb236d36365abfe966eb9e7769896011

tools/layout-checks.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 
 # Copyright 2014 OpenStack Foundation
 # Copyright 2014 SUSE Linux Products GmbH

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 minversion = 1.6
-envlist = pep8,projects,jjb,jenkins-project
+envlist = pep8,projects,jjb,jenkins-project,zuul
 skipsdist = True
 
 [testenv]
@@ -51,7 +51,7 @@ commands =
 
 [testenv:zuul]
 basepython = python2.7
-deps =
+deps = PyYAML
 commands =
   {toxinidir}/tools/run-layout.sh
   {toxinidir}/tools/layout-checks.py