This is the first of multiple updates to ceph-osd where the OSD
init code will be refactored for better sustainability.
This patchset makes 2 changes:
1) Removes "ceph-disk" support, as ceph-disk was removed from the
ceph image since nautilus.
2) Separates the initialization code for the bluestore, filestore,
and directory backend configuration options.
Change-Id: I116ce9cc8d3bac870adba8b84677ec652bbb0dd4
aaa85e3fc5