clean up log fmt usage. Move to log for important data changes,

warnings.

go/storage/needle_read_write.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"log"
 	"os"
 )
 
@@ -26,7 +27,7 @@ func (n *Needle) Append(w io.Writer, version Version) (size uint32, err error) {
 			defer func(s io.Seeker, off int64) {
 				if err != nil {
 					if _, e = s.Seek(off, 0); e != nil {
-						fmt.Printf("Failed to seek %s back to %d with error: %s\n", w, off, e)
+						log.Printf("Failed to seek %s back to %d with error: %s\n", w, off, e)
 					}
 				}
 			}(s, end)