Add open-port and close-port hook commands

[Jim Baker]

Two new hook commands are to be added for opening and closing ports. They
may be executed within any formula hook::

    open-port port[/protocol]

    close-port port[/protocol]

These commands will store in the ZK tree, under **/units/<internal
unit id>/ports**, the desired opened port information as serialized to
JSON. For example, executing ``open-port 80`` would be serialized as
follows::

    {"open": [{"port": 80, "proto": "tcp"}, ...]}