Make GX Workflow Testing More Complete, More Scalable

[jmchilton]

• Add a --library_path argument to create a data library to reuse test data - useful for running against public servers.
• Explicit support for URLs in job description.
• Extend URL/library support to track md5sum of inputs and verification of inputs.
• Add an example with collection inputs, ensure it works (probably doesn't).
• Support nested workflows - requires ephemeris enhancements.
• Allow user mode-only workflow tests.
• Extend Travis CI test template to test only differences.
• Better CLI support for working with traditional Galaxy workflows:
  • Tool to upgrade workflows: Tooling for Upgrading Dependencies in Workflows #779

[bgruening]

• optionally delete workflows/histories after a successful test
• support composite and collection uploads
• support setting dbkey during upload
• only consider workflow_outputs that are also defined in the -test.yml file

[jmchilton]

These are mostly done and if there are existing issues not tracked elsewhere lets create new issues with a modern context.