Note that this can only be used for a cluster with all members in Up status, i.e. use `awaitMembersUp` before using this method. The reason for that is that the cluster leader is preferably a member with status Up or Leaving and that information can't be determined from the `RoleName`.

public void AssertLeader(
	params RoleName[] nodesInCluster
)

member AssertLeader : 
        nodesInCluster : RoleName[] -> unit