Clean up scripts for guest image building

    creates sudoers files in tmp and sets perms before moving it to /etc/sudoers.d
    creates .ssh dir as root then changes perms and ownership to guest user
    creates symlinks to elements files rather than copying them to diskimage-builder

Change-Id: Ib019e46107fab1362d57f5fec3cdb97214764614
Fixes: bug/1100507