sched_downtime: not sure if I was smoking crack, but use the correct user and group variables. Why did this even work in the first place?

Signed-off-by: Christophe Vanlancker <christophe.vanlancker@inuits.eu>
Add check for DRBD

Signed-off-by: Christophe Vanlancker <christophe.vanlancker@inuits.eu>
checkdrbd plugin ought to be a class

Signed-off-by: Christophe Vanlancker <christophe.vanlancker@inuits.eu>