iotop: new package

iotop does for I/O usage what top does for CPU usage.

Signed-off-by: Christophe Vu-Brugier <cvubrugier@fastmail.fm>
Reviewed-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>