Support unit router feature for dubbo， new feature pr： https://github.com/alibaba/dubbo/pull/1438
What problems can this feature solve? case 1: If we have two instance of services or more, we call it serviceA(192.168.0.1), serviceA(192.168.0.2). We want to invoke serviceA (192.168.0.2) first, if serviceA (192.168.0.2) is not available then invoke serviceA (192.168.0.1) automatically. case 2: If we have many relative services, We call it serviceA(192.168.0.1), serviceA(192.168.0.2), serviceB(192.168.1.1), serviceB(192.168.1.2), serviceC(192.168.3.1), serviceC(192.168.3.2) dependencies of service: serviceA -> serviceB -> serviceC We can flexibly build call paths and automatically downgrade calls.
