MB-7532 Set the default value of a rev sequence num to 1.

As the XDCR always expects a positive value for a revision
sequence number, its default value should be initialized to 1.

Change-Id: I6a281ad55d9c5d7e4ed93a6d4e33c609606f7f29
Reviewed-on: http://review.couchbase.org/23964
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Reviewed-by: Jin Lim <jin@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung.seo@gmail.com>