Make BaseEngineTest behave as BaseEngineParTest by default

[jodzga]

When BaseEngineTest is used in multithreaded unit test it will throw exception explaining that perhaps BaseEngineParTest shoul dbe used instead.
It would be better however to make it default by simply renaming:
BaseEngineTest -> BaseIsolatedEngineTest
BaseEngineParTest -> BaseEngineTest
BaseEngineParTest should be just alias to BaseEngineTest and left for backwards compatibility.