private int hostPriority(NodeCandidate other) {
        return Double.compare(this.skewWithThis() - this.skewWithoutThis(),
                              other.skewWithThis() - other.skewWithoutThis());
    }
Returns the host priority, based on allocation skew, of this compared to other
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/provisioning/NodeCandidate.java