The 'ps' command from 'procps-ng' is used in favour of 'ps' from 'busybox'
when 'procps-ng' is installed. The problem is that the outputs are not
compatible and the ‘grep’ is different for further processing. To fix this,
always use the 'ps' command from 'busybox'.
Signed-off-by: Florian Eckert <fe@dev.tdt.de>