ReplicatedPG: correctly handle new snap collections on replica

Backport: bobtail
Signed-off-by: Samuel Just <sam.just@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>
PG: move auth replica selection to helper in scrub

Signed-off-by: Samuel Just <sam.just@inktank.com>
osd_types: add nlink and snapcolls fields to ScrubMap::object

Signed-off-by: Samuel Just <sam.just@inktank.com>
ReplicatedPG/PG: check snap collections during _scan_list

During _scan_list check the snapcollections corresponding to the
object_info attr on the object.  Report inconsistencies during
scrub_finalize.

Signed-off-by: Samuel Just <sam.just@inktank.com>
ReplicatedPG: compare nlinks to snapcolls

nlinks gives us the number of hardlinks to the object.
nlinks should be 1 + snapcolls.size().  This will allow
us to detect links which remain in an erroneous snap
collection.

Signed-off-by: Samuel Just <sam.just@inktank.com>
osd/ReplicatedPG: validate ino when scrubbing snap collections

Signed-off-by: Sage Weil <sage@inktank.com>
osd/PG: fix osd id in error message on snap collection errors

Signed-off-by: Sage Weil <sage@inktank.com>
ReplicatedPG: ignore snap link info in scrub if nlinks==0

links==0 implies that the replica did not sent snap link information.

Signed-off-by: Samuel Just <sam.just@inktank.com>