Follow up on Jetty/Hadoop kerberos principal hostname/realm issues

With the new Jetty SPNEGO brought in with Avatica 1.20.0 +, we have to do some gymnasitics to get Hadoop to accept the principal.

Review why Hadoop won't accept some user/host.name format principals, and whether Jetty stripping the realm from the principal as returned by  is a bug or not.

Also figure out whether having different users with the same username in different realms is even a possibility in Kerberos and Hadoop.