Interface names for /etc/hosts

This file is appended to /etc/hosts in all nodes (osbash and
Vagrant).

It allows users, trainers, and the training-guides to use interface
names that indicate both VM and network (such as controller-mgmt).

Note that only the network node is connected to all networks.

Partial-Bug: 1312764
Implements: blueprint openstack-training-labs
Change-Id: If888537d91ec0ca9c47dc259e61bc438b7f76d05
Merge "Interface names for /etc/hosts"