Use conflicting primaries count in cluster score

This small patch adds the number of conflicting primaries in the cluster
score. This is different from the other non-CV metrics where we usually
compute the percentage of failing instances (for that metric); but for a
somewhat big cluster, 1-2% failing instances will be a too small value
to cause the relocation of conflicting instances (future patches will
also switch other non-CV metrics to this method).