add force delete option of non-empty bucket (#9166)

passing HTTP header `x-minio-force-delete: true` would 
allow standard S3 API DeleteBucket to delete a non-empty
bucket forcefully.

cmd/xl-zones.go

@@ -326,7 +326,7 @@ func undoMakeBucketZones(bucket string, zones []*xlSets, errs []error) {
 		index := index
 		g.Go(func() error {
 			if errs[index] == nil {
-				return zones[index].DeleteBucket(context.Background(), bucket)
+				return zones[index].DeleteBucket(context.Background(), bucket, false)
 			}
 			return nil
 		}, index)
@@ -1232,9 +1232,9 @@ func (z *xlZones) IsCompressionSupported() bool {
 // DeleteBucket - deletes a bucket on all zones simultaneously,
 // even if one of the zones fail to delete buckets, we proceed to
 // undo a successful operation.
-func (z *xlZones) DeleteBucket(ctx context.Context, bucket string) error {
+func (z *xlZones) DeleteBucket(ctx context.Context, bucket string, forceDelete bool) error {
 	if z.SingleZone() {
-		return z.zones[0].DeleteBucket(ctx, bucket)
+		return z.zones[0].DeleteBucket(ctx, bucket, forceDelete)
 	}
 	g := errgroup.WithNErrs(len(z.zones))
 
@@ -1242,11 +1242,26 @@ func (z *xlZones) DeleteBucket(ctx context.Context, bucket string) error {
 	for index := range z.zones {
 		index := index
 		g.Go(func() error {
-			return z.zones[index].DeleteBucket(ctx, bucket)
+			return z.zones[index].DeleteBucket(ctx, bucket, forceDelete)
 		}, index)
 	}
 
 	errs := g.Wait()
+
+	if forceDelete {
+		for _, err := range errs {
+			if err != nil {
+				if _, ok := err.(InsufficientWriteQuorum); ok {
+					undoDeleteBucketZones(bucket, z.zones, errs)
+				}
+
+				return err
+			}
+		}
+
+		return nil
+	}
+
 	// For any write quorum failure, we undo all the delete buckets operation
 	// by creating all the buckets again.
 	for _, err := range errs {