Disable sg-core related tests by default

The sg-core is not required to run Telemetry services. Enabling tests
requiring sg-core by default is not backword-compatible and affects
testing in distributions(eg. RDO) or any users using tempest to
validate their deployments.

Change-Id: Ib08a42f22325d4029b5148f081e1b095fbfc723e
2 files changed