Wip fs cmds

On Thu, 12 Jun 2014, John Spray wrote:
> Although, now that I think about it I wonder if this particular setting
> might be safe-ish to set lazily, as its effect doesn't matter until next
> time OSD map changes to reflect an OSD going out of commission.

The timing is less important, but it needs to be reliable.  I suspect the 
blacklisting is subtlely broken because an ill-timed mon crash/restart 
will lose the update...