注册服务时，加入定制serviceId功能

[sid659]

目前在用1.5.6-Hoxton版，注册服务时，加入定制serviceId，而不是随机生成。

com.huaweicloud.servicecomb.discovery.discovery.MicroserviceHandler.java

public static Microservice createMicroservice(ServiceCombDiscoveryProperties serviceCombDiscoveryProperties) {
...
if (!StringUtils.isEmpty(serviceCombDiscoveryProperties.getServiceId())) {
microservice.setServiceId(serviceCombDiscoveryProperties.getServiceId());
}
...
}