Add guest functions library

This change adds a library of functions that are used by scripts running
inside the node VMs (i.e. scripts located in the scripts directory).

Many of them are specific to either Vagrant or osbash, so they might
get split out later on.

Partial-Bug: 1312764
Implements: blueprint openstack-training-labs
Change-Id: Ieb57e77bb65c562d3674b964af4ac28bc8766c65
Merge "Add guest functions library"