Return false for func that returns bool

Signed-off-by: David Zafman <david.zafman@inktank.com>
Interim working version with backfill reserve state changes

Signed-off-by: David Zafman <david.zafman@inktank.com>
Change waiting_on_backfill to a set<int>

Signed-off-by: David Zafman <david.zafman@inktank.com>
Minor change
Make peer_backfill_info a map which holds a
BackfillInterval for all backfill targets.
Initially see if recover_backfill() can just backfill
the first one and mark them all finished.