Stop logging/printing user token on failed validation

Closes-bug: #2121233

Change-Id: I0d5d0b1b0fc9978d52384a0b74a9b09f83244222
Signed-off-by: Arnaud M <arnaud.morin@gmail.com>

mistral/auth/keystone.py

@@ -35,7 +35,7 @@ class KeystoneAuthHandler(auth.AuthHandler):
             return
 
         if req.headers.get('X-Auth-Token'):
-            msg = 'Auth token is invalid: %s' % req.headers['X-Auth-Token']
+            msg = 'Auth token is invalid'
         else:
             msg = 'Authentication required'