Add schema backward compatibility check when updating store definitions
Adding backwards compatibility checks in AdminClient

For the methods:
* fetchAndUpdateRemoteStore(int nodeId, List<StoreDefinition>
  updatedStores)
* updateRemoteStoreDefList(int nodeId, List<StoreDefinition> storesList)

so the exceptions are thrown even before hitting the server.
Adding schema backwards comaptibility in AdminClient

for these methods:

   * updateRemoteMetadata
   * updateRemoteMetadataPair
   * addStore
minor code review comments