The mergeChunks state of collection_defragmentation.js gets all chunks from config.collections using toArray. If there are a lot of chunks (usually >100 needed) this can require a call to getMore which will fail if the test is being run on a suite that involves stepdowns (concurrency_sharded_with_stepdowns_and_balancer, concurrency_sharded_kill_primary_with_balancer, etc.).

In order to allow the test to continue running on these suites, we should remove the call to toArray and simply check a random subset of the chunks for mergeability in each mergeChunks phase so that getMore is not called.