Allow osbash to enable Vagrant ssh keys

This script can be used to enable access to osbash VMs using the same
ssh key that is used to for logging into Vagrant VMs.

If the script is run from a directory shared with the host, the
downloaded key will be cached.

Partial-Bug: 1312764
Implements: blueprint openstack-training-labs
Change-Id: Ia541e01cabd69f794ea79d8a318f490f518d28ef
Merge "Allow osbash to enable Vagrant ssh keys"