QPID-4739: add ACL tests for new TrustStore + KeyStore objects

Also some small fixups from secondary review: correct exception messages, remove unused imports, tweak a unit test, add a couple of missing licence headers

merged from trunk r1467922


git-svn-id: https://svn.apache.org/repos/asf/qpid/branches/0.22@1469884 13f79535-47bb-0310-9956-ffa450edef68