QPID-4676: add system test to check External authentication provider behaviour  regarding username construction, when specifying or not specifying its useFullDN attribute.

Applied patch by Jakub Scholz

merged from trunk r1463353


git-svn-id: https://svn.apache.org/repos/asf/qpid/branches/0.22@1464456 13f79535-47bb-0310-9956-ffa450edef68