Enable specifying dataset hash in test jobs

[mvdbeek]

Intermediate goal here is that we add hashes to all IWC test job definitions, which would make it easy to re-run all of the IWC workflows using the job cache and find more cornercases where the job cache doesn't work.

How to test the changes?

(Select all options that apply)

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

• I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.