Make sure we actually have a clean VM
Make sure we actually have a clean VM

If a VM is somehow being reused without clean data on it, we can detect
this easily by requeueing if a build.sh file already exists.

final-ci/travis-worker,gavioto/travis-worker,ireznice/travis-worker,gavioto/travis-worker,final-ci/travis-worker,ireznice/travis-worker,travis-ci/travis-worker,travis-ci/travis-worker