Certification

Certification aim is to show if fuel works correctly on specific hardware environment.

Certification is a set of tests that check different openstack environments and scenarios.
We can take fuelweb_test and make them able to run on existing fuel installation.

Implementation:
1. Add option to settings that describes whether to create fuel env or use existing.
2. Move cluster configuration that is hardcoded in tests to yaml config.
We need possibility to modify cluster configuration for certification.
3. Rewrite some methods in FuelWebClient. Create alternative EnvironmentModel for case when we run tests on existing env.
4. Rewrite tests with changes above.