systemd: Wait 5 seconds before attempting a restart of an OSD

systemd: Wait 5 seconds before attempting a restart of an OSD

In commit 92f8ec the RestartSec parameter was removed which now
causes systemd to restart a failed OSD immediately.

After a reboot, while the network is still coming online, this can
cause problems.

Although network-online.target should guarantee us that the network
is online it doesn't guarantee that DNS resolving works.

If mon_host points to a DNS entry it could be that this cannot be
resolved yet and thus fails to start the OSDs on boot.

Fixes: https://tracker.ceph.com/issues/42761
Signed-off-by: Wido den Hollander <wido@42on.com>