tests: Add txn test framework (#5588)

We need a transactional integration testing framework to do some white-box transactional testing. Using this framework, we can easily build a cluster test environment, specify the number of CN, DN, LOG services we need and control the start and stop of these services, and even simulate some network partitioning and error injection

Approved by: @yingfeng, @reusee, @cnutshell, @fengttt