tests: Optimizing kill_daemons() sleep time

tests: Optimizing kill_daemons() sleep time

It could sounds like nothing but the actual sleeping rampup is counter
productive.

The code does : kill <proc>; sleep 0; kill <proc>; sleep 0; kill <proc;
sleep 1; and then it grows up 120 seconds by a smooth rampup.

But actually there is almost no chance the process dies so fast meaning
that by default we switch to the sleep 1.

Moving from sleep 0 to sleep 1 doesn't seems a big win but as
kill_daemons() is called very often we can save a lot of time by then
end.

This patch offer to sleep first a 1/10th of second instead of 0 and then
1/20th of second instead of 0.

The sleep call is also moved after the kill call as it's not necessary
waiting before executing the command.

This patch makes the running time of a test like osd-scrub-repair.sh
dropping from 7m30 to 7m7.

Saving another ~30seconds is an interesting win at make check level.
Signed-off-by: Erwan Velu <erwan@redhat.com>