Enhance port mapping logic, add exposed ports to Host object

[ogajduse]

This PR ensures that broker

1. respects exposed ports in/from the image and then extends them by ports provided in arguments.
2. If port 22 was exposed, changes the hostname of the Host to `the.docker.host.com:.
3. Adds exposed_ports attribute to the Host class if any ports were exposed. Format {"inner-port":"exposed-port"} e.g. {'22': '44263'}