heal: Refactor heal command. (#2901)

- return errors for heal operation through rpc replies.
  - implement rotating wheel for healing status.

Fixes #2491

cmd/xl-v1-bucket.go

@@ -305,27 +305,3 @@ func (xl xlObjects) DeleteBucket(bucket string) error {
 	// Success.
 	return nil
 }
-
-// Heal bucket - create buckets on disks where it does not exist.
-func healBucket(disks []StorageAPI, bucket string) error {
-	bucketFound := false
-	for _, disk := range disks {
-		_, err := disk.StatVol(bucket)
-		if err == nil {
-			bucketFound = true
-		}
-	}
-	if !bucketFound {
-		return traceError(errVolumeNotFound)
-	}
-	for _, disk := range disks {
-		err := disk.MakeVol(bucket)
-		if err == nil {
-			continue
-		}
-		if err != errVolumeExists {
-			return traceError(err)
-		}
-	}
-	return nil
-}