init-radosgw.sysv: Support systemd for starting the gateway

The daemon needs to start under systemd.

Check for systemd running on PID 1. If it is then start
the daemon using: systemd-run -r <cmd>. pidof returns null
as it is executed too quickly, adding 1s of sleep and
script reports startup correctly.

Signed-off-by: JuanJose 'JJ' Galvez <juanjose.galvez@gmail.com>
Merge branch 'wip-rgw-systemd' of https://github.com/jgalvez/ceph into wip-rgw-systemd