`ceph-volume simple activate --all` relies on the presence of json files
in `/etc/ceph/osd` that was created with `ceph-volume simple scan`
command.
In a cluster lifecycle, it is very likely an OSD which was deployed with
ceph-disk at some point gets removed or replaced. It means the corresponding
json file in `/etc/ceph/osd` becomes unrelevant. It makes `ceph-volume
simple activate --all` fails because it tries to mount non existing
partitions.
The idea here is to simply warn the user that the osd described in the
json file doesn't exist anymore and exit properly instead of throwing an
error.