library: add central port func for both "ports" and "expose"

[stavros-k]

Adds support for rendering the expose field. (Partially covers #744)

A new "central" add_port function that based on bind_mode will publish, expose or skip the port.
It also supports setting host_ip per port (#787).
Will expose the host_ip field once migrations are available.

Additionally adds a convenience func for mounting udev as its needed by couple of apps already