vstart/stop: do not loop forever on kill

It may be the case that stop.sh can't stop a process for reasons
unrelated to vstart.sh. Because apache runs independantly, for
instance. Instead of trying forever, try twice in a raw ( should be
enough 99% of the case ) and try three more times, sleeping one second
between each try should be more than enough.

Signed-off-by: Loic Dachary <loic@dachary.org>
Merge pull request #991 from dachary/wip-stop

vstart/stop: do not loop forever on kill

Reviewed-by: Sage Weil <sage@inktank.com>