Marathon continues to try to download resources it can't access

[ssorallen]

When creating a task with a tarball that is not accessible, Marathon retries indefinitely to start the app.

The screenshot below shows Marathon trying to run the following command a bunch of times:

marathon start -i rails-app -C 'cd rails_test_app && bundle exec rails s' \
  -n 1 -c 1 -m 99 -u http://datacentercomputer.s3.amazonaws.com/rails_test_app.tgz

[guenter]

Marathon doesn't have visibility into failing downloads, but the underlying issue is the same as #20. Rate limiting made the issue less severe. Closing this so we can track the issue in #20.