os: FileStore::wipe_subvol: fix removing old dir
os: FileStore::wipe_subvol: fix removing old dir

Older versions of btrfs which don't have BTRFS_IOC_SNAP_DESTROY need to
manually remove snapshots.

Signed-off-by: Colin McCabe <7b35906f1d014e74a9dc8c913eb229119df647aa@dreamhost.com>

ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph