Fuel upgrade backport to 5.0.X

fuel_upgrade_system/fuel_upgrade directory copied from master branch
openstack.yaml is changed according to https://review.openstack.org/#/c/102533/

No other changes were found to fuel-web within https://blueprints.launchpad.net/fuel/+spec/upgrade-to-5-1

blueprint upgrade-to-5-0-1

Change-Id: I6f95863c424fe3d217b635f60509df8065f8a27d