To ensure the new process' parent is pid 1, so systemd won't
complain about supervising a process it does not own.
Fixes the following log spam on reloads:
Apr 25 10:50:54 deb-dev systemd[1]: proxmox-backup.service: Supervising process 1625 which is not our child. We'll most likely not notice when it exits.
Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>