The transactions_write_conflicts.js and transactions_write_conflicts_unique_indexes.js tests run multiple pairs of transactions with writes in various interleavings. In the case that a transaction operation fails for some reason and throws an exception, the test may fail but leave a transaction open. This can lead to problems if we subsequently try to run consistency checks, for example, that require taking strong collection locks. To help this, we should have these tests clean up after themselves in case an exception is thrown, by aborting all transactions or killing the sessions they were using.