CBQE-1594: add incremental upgrade xdcr

Change-Id: I002e390cbaffe5aef737b33cf1f4d7b5ac0f3c85
Reviewed-on: http://review.couchbase.org/29851
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>