Feature to skip specific jobs in automated test runs

[makkus]

In some scenarios it might not be wanted to run example jobs with every automated test invocation (e.g. downloading huge files, or many files on a service that counts downloads to figure out popularity of some datasets).

So it would be good to have a way to mark these, either with a marker token in the job name (like download_file_no_test.yaml), or some other way.