Warn if we are deleting an incomplete layer

... to help diagnosing later possible broken references
to this layer; compare https://github.com/containers/storage/issues/1136 .

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

storage/layers.go

@@ -400,6 +400,7 @@ func (r *layerStore) Load() error {
 					layer.Flags = make(map[string]interface{})
 				}
 				if layerHasIncompleteFlag(layer) {
+					logrus.Warnf("Found incomplete layer %#v, deleting it", layer.ID)
 					err = r.deleteInternal(layer.ID)
 					if err != nil {
 						break