Support explicit ports

It seemed odd to me that after spinning up a grid, I wasn't *sure* of the discoverd address, so this change ensures it is always on port 1111.

This also (I think) allows ports to be explicitly set for scheduled jobs (e.g. if I want to start Redis explicitly on port 6379, I can pass in the `HostConfig` to do that).

This is my first time writing Go, I mainly copied and pasted stuff :wink:

Relates to #5