test: IT fail after change cargo test to cargo nextest

[ben1009]

IT may have concurrency issue, after change test to nextest, can not passed IT, but rollback to cargo test could pass

------------
     Summary [   5.669s] 3/24 tests run: 0 passed, 3 failed, 38 skipped
        FAIL [   2.422s] tikv-client::failpoint_tests txn_cleanup_2pc_locks
        FAIL [   2.616s] tikv-client::failpoint_tests txn_cleanup_async_commit_locks
        FAIL [   3.246s] tikv-client::failpoint_tests txn_cleanup_locks_batch_size
error: test run failed
make: *** [Makefile:26: integration-test] Error 100
Error: Process completed with exit code 2.

[pingyu]

Currently IT cases are running on the same real TiKV cluster. So they would be conflict with each other if running concurrently.

At the beginning of each case, it will clear the TiKV to address the conflicts.

It's not possible to run IT cases concurrently by now. Maybe we can utilize multi-tenancy to isolate the test case in the future.

[ben1009]

close for now, since the behaviour is kind of by design