Fix compile warnings from random key command

Change-Id: I959ac5903d1b01db1076a3837c961f78b1a69710
Reviewed-on: http://review.couchbase.org/30389
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>