Private undertow capability service values expose org.jboss.msc.service.Service methods

Undertow new exposes UndertowService, Server, Host, etc. to other subsystems as service values of public capabilities. However, these objects all implement Service, and thus expose start/stop methods to their dependents. This is poor encapsulation. Ideally, we should extract interfaces from these objects such that the corresponding capabilities only expose methods in explicitly in their contract.