MWEB-1007 Changes in DFS client

The DFS client in `interactive-maps` project does not support ports and it blocks [our load balancer's changes](https://github.com/Wikia/config/pull/668). Changes below once tested and merged to `dev` will unblock config changes.

Changes in DFS client:
* small refactoring, 
* added support for ports,
* and added unit tests.
could we hold default port in Swift.yml file? Pinging @macbre and @ljagiello