waylandshutdown: detect capabilites before listing them all

git-svn-id: https://rebeccablackos.svn.sourceforge.net/svnroot/rebeccablackos@2894 56e3d1a8-0179-4092-b3e2-9fbbcda0c0a9
waylandloginmanager: do the same logical detection as waylandshutdown

git-svn-id: https://rebeccablackos.svn.sourceforge.net/svnroot/rebeccablackos@2895 56e3d1a8-0179-4092-b3e2-9fbbcda0c0a9