cleanup: destroy connections after .Copy() an other one

Everytime a connection is copied with the .Copy() function, it needs to
be destroyed once the object is not needed anymore. This was not done
consistently, a few more locations require the freeing of the connection
resources.

Signed-off-by: Niels de Vos <ndevos@ibm.com>

internal/rbd/rbd_util.go

@@ -1662,6 +1662,7 @@ func (ri *rbdImage) flattenParent(ctx context.Context, hardLimit, softLimit uint
 	if parentImage == nil {
 		return nil
 	}
+	defer parentImage.Destroy()
 
 	return parentImage.flattenRbdImage(ctx, false, hardLimit, softLimit)
 }