Ceph

The current implementation for defining device classes when an OSD is created is by creating the following file:

/var/lib/ceph/osd/<cluster>-<osd-id>/crush_device_class

It would nice to just declare the device class in the JSON that is sent over when creating the OSD instead of using the file.

The ceph-volume implementation is adding support for device class, so this must be addressed before ceph-volume changes.

It would be nice to keep the file name as the key for the JSON, to keep consistency:

{
    "crush_device_class": "value" 
}

Related to ceph-volume Bugzilla issue: https://bugzilla.redhat.com/show_bug.cgi?id=1498521