os/bluestore: don't store/use path_block.{db,wal} from meta

os/bluestore: don't store/use path_block.{db,wal} from meta

This reverts most of 8d07fa5ad0772b4d979dc10695d230074d1f1e69.

ceph-volume goes to great lengths to ensure that the symlinks in the
osd dir are accurate.  Having these values here is an opportunity to
get them out of sync.  And that can happen very easily if the initial
mkfs was performed using a /dev/sdX device name (which is unstable
across reboots).  Even after ceph-volume corrects the symlink, bluestore
will continue to use the stale device path.

Signed-off-by: Sage Weil <sage@redhat.com>