Get fuel version from version.yaml

For upgrades we need to get VERSION from /etc/fuel/version.yaml
instead of hardcoded value defined at time of Puppet run. Falls
back to value set during puppet run in case reading fails.

Depends on https://review.openstack.org/93316

Change-Id: I397a10f00453d593c1a1fde6e5f73645a5c56fa7
Implements: blueprint fuel-containerization-of-services
Related-Bug: #1317049
Merge "Get fuel version from version.yaml"