BUG-1281: switch serialization to use StAX APIs

With the StAX writer in place, we can safely switch the document
serializer utilities to use a simple transformation.

Change-Id: I7e48c1aa8685a536bf36891b0979058258527b9b
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "BUG-1281: switch serialization to use StAX APIs"