[webserver-test] fix one of SpnegoWebserverTest scenarios on macOS

This patch updates SpnegoWebserverTest.TestUnauthenticatedBadKeytab
scenario to adapt to different failure paths on Linux and macOS.
The important invariant stays firm in both cases, though: the server
should respond with HTTP 401.

Change-Id: Ic0da58c9762496446a63d217d8822150fb341b35
Reviewed-on: http://gerrit.cloudera.org:8080/16465
Tested-by: Kudu Jenkins
Reviewed-by: Grant Henke <granthenke@apache.org>
1 file changed