Define constants with NODE_DEFINE_CONSTANT

Change-Id: I9f3a5220de19c05836be578a7a146bb5b3379df7
Reviewed-on: http://review.couchbase.org/28616
Reviewed-by: Brett Lawson <brett19@gmail.com>
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>