Improve unit tests for DB archiving.

Test all tables that have a uuid column and no constraints that make
generic testing difficult, rather than just a couple of tables.

Make the teardown code more generic.

Add test_archive_deleted_rows_2_tables, which tests that we can
archive rows from two tables in one call.

Change-Id: If08aac3c6869820c72dfcb1bf6d22d19c2995c8a
Merge "Improve unit tests for DB archiving."