Support binding Service Discovery to specific IP or hostname

Now it's possible to specify where to bind the mDNS service to. Previously it would use whatever Java returned as the local host address. On multi interface systems that could cause problems as it sometimes would bind to the wrong interface.
since bind_addr is a unique key and will occur only once this while structure is not necessary. Please see examples (like HueBinding) to see how to use the ManagedService in that case.