Nodepool scripts

They are use to prepare ubuntu image: install packages, dependecnies,
add ssh keys. 

Python files were borrowed from Openstack infra repository. And there is a small modification in cache_devstack.py that makes it install deb packages one by one (was all in one install command). It helps to avoid failing if there is a wrong package name.
The cache_devstack.py was copied as it from openstack infra repository