organize tests

[kkamdin]

Assigned this one to myself, I'll do it as a follow to up #60 .

This came up when reviewing David's PR: #60 (comment).

I think it would be nice to move the tests for each beamline into their own folder with this directory structure.

orchestration/
├── flows/
│   ├── bl733/
│   │   ├── __init__.py
│   │   ├── move.py
│   └── bl832/
│       ├── __init__.py
│   │   ├── move.py
└── tests/
    ├── test_bl733/
    │   ├── __init__.py
    │   ├── test_move.py
    └── test_bl832/
        ├── __init__.py
        └── test_move.py

That way we can also put your MockGlobusComputeClient in a shared location at the test level or a in a shared pytest fixture, and you can run tests for each beamline separately more easily. Would that work? What do you think?

I don't think it needs to be part of this PR though. Just a follow up after this is merged.