Support both dynamic mgmt & http ports

Using both port 0 for management.server and server causes the following stack trace in 2.1.1.RELEASE:

Stacktrace

java.lang.IllegalArgumentException: createCheck port must be greater than 0
	at org.springframework.util.Assert.isTrue(Assert.java:118) ~[spring-core-5.1.6.RELEASE.jar:5.1.6.RELEASE]
	at org.springframework.cloud.consul.serviceregistry.ConsulAutoRegistration.createCheck(ConsulAutoRegistration.java:236) ~[spring-cloud-consul-discovery-2.1.1.RELEASE.jar:2.1.1.RELEASE]
	at org.springframework.cloud.consul.serviceregistry.ConsulAutoRegistration.setCheck(ConsulAutoRegistration.java:129) ~[spring-cloud-consul-discovery-2.1.1.RELEASE.jar:2.1.1.RELEASE]
	at org.springframework.cloud.consul.serviceregistry.ConsulAutoRegistration.initializePort(ConsulAutoRegistration.java:336) ~[spring-cloud-consul-discovery-2.1.1.RELEASE.jar:2.1.1.RELEASE]
	at org.springframework.cloud.consul.serviceregistry.ConsulAutoServiceRegistration.getRegistration(ConsulAutoServiceRegistration.java:58) ~[spring-cloud-consul-discovery-2.1.1.RELEASE.jar:2.1.1.RELEASE]
	at org.springframework.cloud.consul.serviceregistry.ConsulAutoServiceRegistration.getRegistration(ConsulAutoServiceRegistration.java:33) ~[spring-cloud-consul-discovery-2.1.1.RELEASE.jar:2.1.1.RELEASE]
	at org.springframework.cloud.client.serviceregistry.AbstractAutoServiceRegistration.start(AbstractAutoServiceRegistration.java:137) ~[spring-cloud-commons-2.1.1.RELEASE.jar:2.1.1.RELEASE]
	at org.springframework.cloud.consul.serviceregistry.ConsulAutoServiceRegistration.start(ConsulAutoServiceRegistration.java:73) ~[spring-cloud-consul-discovery-2.1.1.RELEASE.jar:2.1.1.RELEASE]
	at org.springframework.cloud.consul.serviceregistry.ConsulAutoServiceRegistrationListener.onApplicationEvent(ConsulAutoServiceRegistrationListener.java:63) ~[spring-cloud-consul-discovery-2.1.1.RELEASE.jar:2.1.1.RELEASE]

Issue tracing

Tracing through, the issue lies in org.springframework.cloud.consul.serviceregistry.ConsulAutoRegistration#getManagementPort which defers to org.springframework.cloud.client.discovery.ManagementServerPortUtils#getPort, which in turn returns 0 as ManagementServerProperties.port is 0.

Appreciate this is more likely an issue with spring-cloud-commons (where ManagementServerPortUtils is defined), but raising here for visibility for others who may stumble down this path

application.yml

management:
  server:
    port: 0

server:
  port: 0

Application

@SpringBootApplication
@EnableDiscoveryClient
public class DemoWebServicesApplication {
    public static void main(String[] args) {
        SpringApplication.run(DemoWebServicesApplication.class, args);
    }
}

Start in ConsulAutoRegistration#getManagementPort and follow its call to ManagementServerPortUtils#getPort, using the reported application.yml with both management.server.port and server.port set to 0. Reproduce the startup failure and inspect how the management and HTTP ports are selected for the Consul health check. Done means an application using both dynamic ports starts without the createCheck port error and registers correctly.