osd: fix rescrub after repair

We were rescrubbing if INCONSISTENT is set, but that is now persistent.
Add a new scrub_after_recovery flag that is reset on each peering interval
and set that when repair encounters errors.

Signed-off-by: Sage Weil <sage@inktank.com>
mon: note scrub errors in health summary

Signed-off-by: Sage Weil <sage@inktank.com>