Add error msg: bad image upload

[meryl-spencer]

When submitting solutions there is no check/ error message if you try and submit a non-existent image. This can be seen in submission number: 2e8dbca8-7e5a-4c65-a101-e57e94879813 in which the docker image url was 'notarealimageurl'.

The submission starts and goes through at least the 'launching pods with no errors' stage before finally ending 2-3 hours latter with 'Terminated Error: InitializationFailed' with no indication of why the initialization failed. It would be a time saver to have some sort of indication that the user tried to submit an invalid image in the error logs, especially if the check could circumvent some of the startup time.

As background I noticed this problem because all of my recent runs have failed to initialize and I am trying to work out what the issue is. I purposely submitted a bad image to see if would give me an error message, so I could rule out that my images hadn't been uploaded correctly.

[nkoenig]

There is a tool you can use to test your submission before running it on Cloudsim. See https://github.com/osrf/subt/wiki/Cloudsim-Docker-Compose.

This should allow you to iterate more quickly.