Support Silicon for retrieval of entity ownership information

Support Silicon for retrieval of entity ownership information

ClusterEntities.py uses RPC introduced in Phosphorus to retrieve
entity ownership information, hence Silicon or earlier versions,
which store entity ownership information in the data store,
are not supported.

Fall back on the REST API calls to retrieve the information from
the operational data store, if the status code for the RPC call is
400 (bad request), to support Silicon and earlier versions.

Signed-off-by: Sangwook Ha <sangwook.ha@verizon.com>
Change-Id: I18c8d667554d25e5126770235ad33ff404cbe9fe