XD-464 Add XD on Yarn functionality.

NOTE: MarkP wanted me to add this pull request so that it gets general visibility and we have something to work on. Branch this stuff is based on may be used in springone demos. 

Build script creates xdapp.zip which contains the whole Yarn app.
New yarn command set for XD shell, added config command for Yarn
resource manager. Modified AdminServer to play nice with embedded
application contexts and set tomcat to choose its free port.