protected int getDefaultPortFromScheme(String scheme) {
        if (scheme == null) {
            return -1;
        }
        if (scheme.equals("http")) {
            return 80;
        } else if (scheme.equals("https")) {
            return 443;
        } else {
            return -1;
        }
    }
Get the default port of the target server given the scheme of vip address if it is available. 
Subclass should override it to provider protocol specific default port number if any.

@param scheme from the vip address. null if not present.
@return 80 if scheme is http, 443 if scheme is https, -1 else.
ribbon-loadbalancer/src/main/java/com/netflix/loadbalancer/LoadBalancerContext.java