#359 LifecycleTest: implement and use MkStep and MkScenario

Please review and apply.

Also I'm not sure about `incrementsTransactionCount()` test: before my change it  checked that `Txn.increment()` was invoked, but now it doesn't. Is it ok? If not then please hint about how to do it because Base now is a real class and its txn() method returns fake instance of Txn instead of mocked version from Mockito.