Adding configuration to specify wsdl_hostname to be used in distributed ...

Hello, I'd like to contribute with a little but useful change. Recently I needed to serve my webservices to SOAP format and I used your lib. Thanks about that. 
So I had a problem when I needed to serve the same webservice in a round-robin configuration. I have a main domain to access the webservice appointing to three machines running the SOAP Server. 
When a user sent a request to the server, ocurred a problem, cause the tornadows answered the server IP in WSDL, not the main domain that the user had configured. 
To fix this problem I made a little change and documented it, as you can take a look. It's gonna be useful to many people that has an architecture like mine.
If you think that it is pertinent, feel free to include the changes to the project.

Thanks!