Fix unit tests for fetching related Rancher cluster.
Fix unit tests for fetching related Rancher cluster.

opennode/waldur-mastermind,opennode/waldur-mastermind,opennode/waldur-mastermind,opennode/waldur-mastermind,opennode/nodeconductor-assembly-waldur,opennode/nodeconductor-assembly-waldur,opennode/nodeconductor-assembly-waldur