THRIFT-2880 Read the network address from the listener if available.

Often in tests, the listening port of a test server is automatically
selected by passing the zero port in the host, as in "127.0.0.1:0".
An example of such behaviour is in the "httptest" package of the
standard library:

https://github.com/golang/go/blob/master/src/net/http/httptest/server.go#L65

As such, it is necessary to read from the listener itself to retrieve
the actually listening port, as in

https://github.com/golang/go/blob/master/src/net/http/httptest/server.go#L107