test: hsr: Call cleanup_all_ns when hsr_redbox.sh script exits

Without this change the created netns instances are not cleared after
this script execution. To fix this problem the cleanup_all_ns function
from ../lib.sh is called.

Signed-off-by: Lukasz Majewski <lukma@denx.de>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>