[LIB_JOOMLA] only run admin enabled auth plugins when logging into the backend
[LIB_JOOMLA] only run admin enabled auth plugins when logging into the backend

zweidner/hubzero-cms,zweidner/hubzero-cms,anthonyfuentes/hubzero-cms,zweidner/hubzero-cms,anthonyfuentes/hubzero-cms,zooley/hubzero-cms,zooley/hubzero-cms,zooley/hubzero-cms,anthonyfuentes/hubzero-cms,zweidner/hubzero-cms,zooley/hubzero-cms,anthonyfuentes/hubzero-cms