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

Closes-Bug: #1253074

Change-Id: Ia531f73f98418594f867f3c2849865c26b13e18d
Merge "Added a check for HTTP_X_IDENTITY_STATUS"