This commit changes the behavior of the port check to check all possible
IPv4 network interfaces when the host IP is `nil` or `0.0.0.0`. This
means that if the desired port is available on any network interfaces, a
forward from 0.0.0.0 will use that interface.
If the port is open (in use) on all interfaces, then it's treated as a
collision and will either throw an error or auto-correct the port, based
on the Vagrantfile configuration.
d4acdd06ec