Expertise Testing: Reduce cross-file and cross-test dependencies

[haroldrubio]

Refactor the tests to no longer have the following behavior:

• All tests must happen after test_create_conference.py and test_create_journal.py - these tests just serve to create the data, any tests done at this level are already done in openreview-py
• Remove dependency of expertise selection edges made in test_create_dataset.py in test_expertise_service.py (There are other dependencies of this form across the other tests)
• Test job cases end-to-end in a single test to avoid cascading failures (request to retrieving results should be done in a single test)