Enhance the test coverage part-12: dubbo-registry/dubbo-registry-multicast(dubbo-registry-redis|dubbo-registry-zookeeper)

[lovepoem]

Add unit test to the modules:
dubbo-registry/dubbo-registry-multicast
dubbo-registry/dubbo-registry-redis
dubbo-registry/dubbo-registry-zookeeper

[kun-song]

Let me try this :)