Add an appropriate default option for BTRFS, so those types of OSDs can be more easily created.
Add an appropriate default option for BTRFS, so those types of OSDs can
be more easily created.

Signed-off-by: Mike Shuey <ad61365375f1c0fead87382933701f5f56652f9c@purdue.edu>

fmeppo/ceph-docker,ceph/ceph-docker,dmitryint/ceph-docker,mkkie/ceph-docker,JrCs/ceph-docker,AcalephStorage/ceph-docker,osixia/ceph-docker,AcalephStorage/ceph-docker,fmeppo/ceph-docker,fmeppo/ceph-docker,dmitryint/ceph-docker,osixia/ceph-docker,mkkie/ceph-docker,rootfs/ceph-docker,cdxvirt/ceph-docker,ceph/ceph-docker,JrCs/ceph-docker,dmitryint/ceph-docker,JrCs/ceph-docker,cdxvirt/ceph-docker,osixia/ceph-docker,rootfs/ceph-docker,AcalephStorage/ceph-docker