Skip tests based on service features disabled in tempest

It's not possible to know if services have certain features
enabled from the sevice API in certain cases. Let's leverage
the service specific feature groups in tempest. If a specific
service feature is disabled in tempest config, the decorated
tests would be skipped.

ex. If tempest.conf contains

[volume-feature-enabled]
backup = False

test_cinder_volume_create_backup_restore scenario test would be
skipped.

Change-Id: I7a2495182791595c87f8245ff5e13dfd841b013f
2 files changed