Upgrade system via apt

This script upgrades the installed packages in an apt-based system.
After a kernel upgrade, the old kernel is removed (in order to save
space), and so are packages and package files that are no longer needed.

Partial-Bug: 1312764
Implements: blueprint openstack-training-labs
Change-Id: Iaadcebc424572787d3a2d77f6b19ab636d65ee58