ensure ClusterInfo is always reachable by retrieving it via ClusterManager

For now, ClusterInfo can be obtained via Cluster.Info(). This is problematic since underneath it uses the ConfigurationProvider to obtain the data, and only HttpStreamingProvider actually retrieves it.
So if CarrierPublicationProvider is used, cluster info is in effect unavailable.
Furthermore, this path is used because the REST endpoint that provides the configuration is password-protected.

The only sureproof way of getting cluster info, without dependency to the configuration provider used, is probably to put the API at the ClusterManager's level (since accessing the manager requires the user to authenticate). There's already an ClusterInfo method here returning IResult<Pools>, that should be replaced with IResult<ClusterInfo>.