osd: write (empty) log, bounds on remove_pg start
osd: write (empty) log, bounds on remove_pg start

This zeros the log, and the bounds, when we start pg removal.  Previously
we just removed the log and didn't write the (empty) bounds, breaking
cosd startup later when the old bounds are totally wrong.

Signed-off-by: Sage Weil <6dd34506bbd5e58221bbb3e4732d97c91f02277b@newdream.net>

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