preload.sh: If this script was ran before implementing the rce/docker fix, cleanup
preload.sh: If this script was ran before implementing the rce/docker fix, cleanup

Signed-off-by: Andrei Gherzan <8dc7c09356db0b1762fb140617d7375c0a5a4131@resin.io>

resin-io/resin-preload-image-script,resin-io/resin-preload-image-script