If the src directory or any of its descendant is snapshottable and the dst directory or any of its ancestors is snapshottable, we consider this as nested snapshot, which should be denied. Reviewed-by: Shashikant Banerjee <shashikant@apache.org> (cherry picked from commit de6b8b0c0b1933aab2af3e8adc50a2091d428238) (cherry picked from commit c9fc118991104acf9109aa769fe1a0e84f425a61)