Run tests against several servers and implement blocklist

Benefits:

1. ensures that iwc WFs are usable on more public Galaxy instances
2. helps discover differences in installed tools on usegalaxy.* instances

We could start by testing on usegalaxy.org *and* usegalaxy.eu.

WFs that are known to run only on a specific server could have an accompanying blocklist in their tests (one option could be in the form of comment lines in the test.yml file).

Start by reviewing the workflow tests and their test.yml files, then run them against usegalaxy.org and usegalaxy.eu to compare behavior and installed-tool differences. Define how server-specific blocklists should be represented in test.yml; done means the test suite covers both instances and known server limitations are recorded and respected.

Written by the indexing model from the issue text.