MB-10047:  xdcr-demand-encryption can only be 0 or 1

Change-Id: Ibf53256850173826f3c8e40018966b02d666030b
Reviewed-on: http://review.couchbase.org/35690
Reviewed-by: Bin Cui <bin.cui@gmail.com>
Tested-by: Bin Cui <bin.cui@gmail.com>