Update old-format OSTs when they are first mounted by b_devel code.

Update old-format OSTs when they are first mounted by b_devel code.
- convert O/R/* to O/0/* and put fsd_last_objid into O/0/LAST_ID
- don't use the "VERSION" file but instead set an incompat flag on the OST
  so we can't mount it on old systems again and create new/empty O/R dirs
  and start creating objects in there (lustre checked compat flags for ages)
- don't write out filter server data anymore - we write to LAST_ID instead
- set an rocompat flag on the MDS for b_devel because lov_objids isn't checked
  by old lustre code and we would delete valid objects if we regressed to the
  old code and created objects
b=2097
r=phil