Stop adding "http://localhost:5000" to empty IServerAddressesFeatures

[halter73]

Servers such as Kestrel and HttpSysServer should define their own default listening endpoints (which will likely still listen on port 5000) so that the servers don't have to assume that a single address of "http://localhost:5000" indicates that no listening endpoint has been configured.

Here is the relevant line of code

[halter73]

aspnet/KestrelHttpServer#1312 is Kestrel's reaction to this proposed change. The Kestrel PR can be merged first, since adding "http://localhost:5000" to IServerAddressesFeature only results in a warning.

[shirhatti]

@Tratcher Do we have an issue to react to this in HttpSysServer as well?

[Tratcher]

aspnet/HttpSysServer#297