scanner: Primary key returned should be raw bytes

Change-Id: I6c06c97898fd4a90152ee0828544abbdc825c869
Reviewed-on: http://review.couchbase.org/43480
Reviewed-by: Sarath Lakshman <sarath@couchbase.com>
Tested-by: Sarath Lakshman <sarath@couchbase.com>