[gluster] log killall failures at info level

Failing to send a signal to the gluster daemons will happen on
any system with gluster installed but not running; don't log it
at warning level.

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>
[systemd] add journalctl --list-boots output

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>