Make it possible to set the root node

Change-Id: Iaab5b1900d68e8ad7d1a17f32ab185ad30cf8f4d
Reviewed-on: http://review.couchbase.org/40135
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Volker Mische <volker.mische@gmail.com>