Rework tests

[adorton-adobe]

We're overhauling the User Sync Tool's testing infrastructure.

Rationale:

• pytest is preferable to nose - much simpler to use and powerful, flexible fixture system
• Testing framework for black box tests is confusing, difficult to use and doesn't integrate with CI systems
• 99% of what we can do in the black-box framework can be done as unit tests (by targeting app.main(), the entrypoint used by the pex build)

Changes in this update:

• Remove old tests/ directory (if needed, can get old tests in v2.4)
• Remove test_framework/ (any components we might need can be obtained in v2.4)
• Define a few new tests in tests/ directory
• Update setup and test dependencies in setup.py
• Configure to run pytest with python setup.py test
• Enable coverage reporting
• Fixture files for base config files
• Define fixtures to get base fixture directory and to get & modify base config files
• Refactor LDAP connector to isolate configuration option handling so we can test it
• Modify CI config and scripts to run tests

Rough roadmap:

• Define fixtures to mock UMAPI (we'll probably want to use the vcr.py-based mock server from the old test_framework)
• Define fixtures to mock LDAP (once we switch to ldap3 as per Switch to ldap3 #436, we can use its mock LDAP server)
• Create a few tests that run the pex file to make sure the build succeeds. We'll need to integrate this with the CI builds and make these tests optional to run locally

[adorton-adobe]

We may not need the mock UMAPI server, there's an plugin that integrates vcr.py and pytest:

https://pytest-vcr.readthedocs.io/en/latest/