rtcwake: clean up usage

Signed-off-by: Karel Zak <kzak@redhat.com>
schedutils: don't apply -a without -p

The unsuspecting user might use taskset -a mask command. Behavior then
is to exec with no affinity applied at all. Better handled by ignoring
all_tasks if no pid was given.

Signed-off-by: Daniel Stodden <daniel.stodden@gmail.com>