Service name should be taken from Discovery Info Port Name

[janisz]

Marathon and Mesos allows specifying names for port. We should use this name to register service in Consul. We can remove consul: <name> label and keep only service tags in Marathon. If service does not have port name it will not be registered.

• https://github.com/apache/mesos/blob/1.0.0/include/mesos/mesos.proto#L1920-L1921
• https://github.com/mesosphere/marathon/blob/31426bd1f7b091b78748ea7fd83c497db3dfea9e/docs/docs/ip-per-task.md#service-discovery