Added a check for HTTP_X_IDENTITY_STATUS

If keystone is configured to run in 'delay_auth_decision' mode it will
pass the token, along with the HTTP header X-Identity-Status set to
'Invalid'. This check for this, and returns a 401

Change-Id: Ib57ccd1f40ecca0f05197f1b4677eb3e3cd24969
Closes-Bug: #1253074