Return WWW-Authenticate Header in ShutdownHandler

**12.1.9**

**Make Jetty ShutdownHandler return a correct HTTP-Header on token mismatch. Currently no WWW-Authenticate Header is returned, resulting in the Jetty HTTP-Client to throw an error as the protocol is violated**

Start at Jetty's ShutdownHandler and trace the response produced when the shutdown token does not match. Reproduce the mismatch with the HTTP client, then verify that the response includes a WWW-Authenticate header and the client no longer reports a protocol violation.

Written by the indexing model from the issue text.