CBD-1425:  change BLANKFILE from "''" to '""'

Change-Id: Ibc4a310026b16c9b611c6b80df79eac3025308ef
Reviewed-on: http://review.couchbase.org/40634
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>