Tidy up index creation and cleanup in tests

Use create_test_indexes and clean_test_indexes instead of a variety of
calls to create or delete individual indexes.

This fixes some occasional fails; some tests were only passing if other
tests ran first and left "metasearch-test" indexes around.  After this
commit, the tests should all create the indexes they need, and clean up
properly after themselves, so failures should be more deterministic.