- collect all conflicting layouts, not just the first, so a vid spanning
three layouts does not leave one writable
- mark quarantine on the location list only: folding it into the stored
report made the volume digest permanently disagree with the server and
forced a full volume list every heartbeat
- isAllWritable now honors the location read-only mark so a quarantined
copy stays out of writables through resyncs and re-registration
- re-check the conflict before keeping marks, and do not clear a node's
quarantine while it still holds the vid in another layout
- log the full layout keys on both sides of the conflict