Move and re-enable test_build_configuration_branch tests

This renames the TestSchedulerMergeModes -> TestSchedulerMerges
and moves some other tests that deal with merge behavior to there:

  * test_build_configuration_branch -> test_merge_branch
  * test_build_configuration_multi_branch -> test_multi_branch

Story: 2000773
Task: 3424

Change-Id: I213cd8036addd11ee9d227f94a2ae21b9a168413
7 files changed