Comment 0 for bug 1516140

While writing the documentation I noticed that Juju has a `opened-ports` command to return the ports that are opened. This would be very useful in python and we should have a chram helper for this command.

# opened-ports -h
usage: opened-ports [options]
purpose: lists all ports or ranges opened by the unit

options:
--format (= smart)
    specify output format (json|smart|yaml)
-o, --output (= "")
    specify an output file

Each list entry has format <port>/<protocol> (e.g. "80/tcp") or
<from>-<to>/<protocol> (e.g. "8080-8088/udp").