Scripts to configure yum and upgrade system

The first script in this changeset configures yum to use a proxy (if
VM_PROXY is set) and adds the RDO repo.

The second script updates the packages installed in a yum-based system.

Partial-Bug: 1312764
Implements: blueprint openstack-training-labs
Change-Id: Iad42b6aad2bf48329cb2c3bb2bc7a1d698d9c608