ReplicatedPG: start scanning omap at omap_recovered_to

Previously, we started scanning omap after omap_recovered_to.
This is a problem since the break in the loop implies that
omap_recovered_to is the first key not recovered.

Backport: bobtail
Signed-off-by: Samuel Just <sam.just@inktank.com>
ReplicatedPG: correctly handle omap key larger than max chunk

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