fuel-upgrade: use extended markup for fixtures

Since now the Fuel-Upgrade script supports extended YAML syntax
for loading fixtures. That means we can create new releases.yaml
based on openstack.yaml from the Fuel repo.

Implements blueprint upgrade-to-5-1

Change-Id: I01bcf26efe681cb767290e9e57ffe0e7e425d0be
Merge "fuel-upgrade: use extended markup for fixtures"