QPID-3981: Windows C++ Broker fails ACL self tests

Most failures caused by a bug in NullAuthenticator, it was not adding the
default realm to user IDs that didn't already have a realm. This fixes 20 of the
23 failures for this test, 3 tests are still failing:

16: acl.ACLTests.test_connection_limits_by_ip_address ....................... fail
16: acl.ACLTests.test_connection_limits_cli_sets_all ........................ fail
16: acl.ACLTests.test_queue_per_user_quota .................................. fail

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1548268 13f79535-47bb-0310-9956-ffa450edef68