osd: make automatically marking of unfound as lost optional

osd: make automatically marking of unfound as lost optional

We may not want to do this automatically until we have more confidense in
the recovery code.  Even then, possible not.  In particular, the OSDs may
believe they have contact all possible homes for the data even though there
is some long-lost OSD that has the data on disk that if offline.

For now, we make the marking process explicit so that the administrator can
make the call.

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