Fix Ceph OSD not starting after reboot with loop device

[mandre]

The ceph-osd-losetup service sets up the loop device backing the Ceph OSD, but after a reboot two things can go wrong:

1. LVM scans run before the loop device is ready, so the vg_ceph logical volumes (data, db) are never activated. The OSD fails with: 'failed to open /dev/vg_ceph/data: No such file or directory'

2. Ceph services can start before the losetup service completes, racing against the loop device setup.

Fix both by adding:

• ExecStartPost=vgchange -ay vg_ceph to activate the LVs after the loop device is attached
• Before=ceph.target to ensure correct ordering with all Ceph daemons