GetJournalEditServlet fails to authorize valid Kerberos request

GetJournalEditServlet uses request.getRemoteuser() to determine the remoteShortName for Kerberos authorization, which fails to match when the JournalNode uses its own Kerberos principal (e.g. jn/<hostname>@<realm>).

This can be fixed by using the UserGroupInformation provided by the base DfsServlet class using the getUGI(request, conf) call.