BUG-509: StoreUtils should operate on NormalizedNode

This prunes the use of MetadataNode from StoreUtils. It turns out it is
completely unnecessary. This removes the last user of
Metadata.getChildren(), which will be removed in a subsequent patch.

Change-Id: I778e77b826576b8fa53e040a825d615dab7d253f
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "BUG-509: StoreUtils should operate on NormalizedNode"