Change how fuel-library noop hiera overrides work

[Aleksandr Didenko]

It's about https://github.com/openstack/fuel-noop-fixtures/blob/master/doc/usage.rst#using-hiera-and-facts-overrides

Putting an override will change how rpec test works, so basically we're losing the ability to run the same test for the same astute.yaml fixture WITHOUT override.

How to reproduce:
run a tests with hiera override in https://github.com/openstack/fuel-noop-fixtures/tree/master/hiera/override/

Expected result:
tests is executed twice: for vanilla configuration data and for data with override

Actual result:
tests is executed once with configuration data override

This is applicable to 9.0+ only

[Matthew Mosesohn (raytrac3r)]

This looks like tech debt and not a real bug