Move dagster-celery-tests functions to utils and pipelines to repo.py
Move repeated functions into utils.
Move pipeline defs to separate repo.py. Since they are loaded via file, any relative imports would break in the test files otherwise.
Test Plan: Not great, a lot of these tests fail locally and are skipped in BK
Reviewers: catherinewu, nate, alangenfeld
Reviewed By: alangenfeld
Differential Revision: https://dagster.phacility.com/D4046