Per-host network interface configuration

Adds support for configuration of per-host network interfaces in Kolla Ansible.
Previously, all interfaces were configured in globals.yml, meaning that all
hosts used the same interface names. Now, interfaces are configured for each
host via inventory files.

This does have the drawback that host entries in the inventory are rather long
and not too readable. An improvement on this could be to generate host_vars
files. With a little more intelligence, it would be possible to use group_vars
files or even globals.yml when interfaces are uniform within a group or
globally.

Change-Id: I95a128d762ff9faf70467f83cb276a5ab619d1ea
Story: 2001658
Task: 6691