remove all bucket metadata

fix https://github.com/chrislusf/seaweedfs/issues/2118

weed/filer/filerstore_wrapper.go

@@ -23,6 +23,7 @@ type VirtualFilerStore interface {
 	AddPathSpecificStore(path string, storeId string, store FilerStore)
 	OnBucketCreation(bucket string)
 	OnBucketDeletion(bucket string)
+	CanDropWholeBucket() bool
 }
 
 type FilerStoreWrapper struct {
@@ -42,6 +43,13 @@ func NewFilerStoreWrapper(store FilerStore) *FilerStoreWrapper {
 	}
 }
 
+func (fsw *FilerStoreWrapper) CanDropWholeBucket() bool {
+	if ba, ok := fsw.defaultStore.(BucketAware); ok {
+		return ba.IsDropBucketAltogether()
+	}
+	return false
+}
+
 func (fsw *FilerStoreWrapper) OnBucketCreation(bucket string) {
 	for _, store := range fsw.storeIdToStore {
 		if ba, ok := store.(BucketAware); ok {