Updated port function 

1st stab at updating the port function in order to parse the new NetworkSettings Ports dictionary and account for advanced redirects introduced in 0.6.5

- Returns a list of IP/ports combinations, which is pretty much what the API returns. For example:
  ```
[{u'HostIp': u'127.0.0.1', u'HostPort': u'4567'}] 
```
- Added unit test and integration test

Should the port function take an IP argument so we can return just the port vs the IP/Port combination?