Fix issue with old ceph-disk-prepare

Old ceph-disk-prepare re-write the partition table and fail before writting
the Parition GUID.
This fix test the presence of a osd device status, if present, we skip
this OSD.
It also fix a typo when setting the osd_device status

Signed-off-by: Alexandre Marangone <alexandre.marangone@inktank.com>