Build fails due to test interactions: data not being cleaned consistently

Very similar in spirit to CONTINUUM-2736, tests are not well-behaved which is leading to build instability. On continuum-ci.a.o, I noticed the builds were consistently failing despite the full test suite comprehensively passing locally.

The problem is visible in the build results as the test failure:

Results :

Failed tests:   testRemoveRepository(org.apache.continuum.repository.DefaultRepositoryServiceTest): check # repositories expected:<1> but was:<2>

Tests run: 150, Failures: 1, Errors: 0, Skipped: 0