Give better tox output

One of the tests would output stderr and it would not be captured by tox

resulting in output like this http://paste.openstack.org/show/616128/
The tests are working fine but that output gives a false impression to the
developer that something is wrong

I captured the stderr during that test so that would not show.

Change-Id: I7f76da0cb1a57280848d7d831e2a686e4ec5c81a

mistralclient/tests/unit/v2/test_cli_action_execs.py

@@ -16,6 +16,9 @@
 
 import copy
 import json
+import sys
+
+from six import StringIO
 
 import mock
 
@@ -153,6 +156,10 @@ class TestCLIActionExecutions(base.BaseCommandTest):
     def test_update_invalid_state(self):
         states = ['PAUSED', 'WAITING', 'DELAYED']
 
+        # Redirect the stderr so it doesn't show during tox
+        _stderr = sys.stderr
+        sys.stderr = StringIO()
+
         for state in states:
             self.assertRaises(
                 SystemExit,
@@ -161,6 +168,10 @@ class TestCLIActionExecutions(base.BaseCommandTest):
                 app_args=['id', '--state', state]
             )
 
+        # Stop the redirection
+        print(sys.stderr.getvalue())
+        sys.stderr = _stderr
+
     def test_list(self):
         self.client.action_executions.list.return_value = [ACTION_EX]