@Override
  public void flush() {
    metadataStore.flush();
  }
Instantiates the {@link NamespaceAwareCoordinatorStreamStore} based upon the provided
MetadataStore that is instantiated and the namespace.

@param metadataStore the instantiated {@link MetadataStore}.
@param namespace the namespace to use for storing the keys in the metadata store.
samza-core/src/main/java/org/apache/samza/coordinator/metadatastore/NamespaceAwareCoordinatorStreamStore.java