set serviceMap for lightCluster after first time service discovery

[GavinChenYan]

In the LightCluster, it will try to get the service urls by service Id from serviceMap cache

    List<URL> urls = serviceMap.get(serviceId);

If it is not existing, go to consulRegistry to do service discovery.

But the discovery result should be set to serviceMap cache.

[stevehu]

set serviceMap for lightCluster after first time service discovery light-4j master

[stevehu]

set serviceMap for lightCluster after first time service discovery light-4j 1.6.x