Switch back to ZKConnectionRegistry by default at least in test

For now, MasterRegistry can not deal with master restart, as it can not load the new master address automatically.

I see there is a invalidateConnection method in HBaseTestingUtilities but it needs a very big refactoring to make all the UTs work like this.

So here I suggest we switch back to ZKConnectionRegistry by default, and open a new feature branch to finish the TODOs and the refactoring on UTs.

As now it is already a big problem for me as I want to merge a feature branch back to master but the state of UTs are a mess.