westonlaunchcaller: add support for waiting for the host wayland server to start, before starting the 'guest' session, so it doesn't fail

git-svn-id: https://rebeccablackos.svn.sourceforge.net/svnroot/rebeccablackos@2780 56e3d1a8-0179-4092-b3e2-9fbbcda0c0a9