@Override
    public boolean apply(@Nullable PredicateKey input) {
        return delegate.apply(input);
    }
A predicate that is composed from one or more predicates in "AND" relationship.
It also has the functionality of "fallback" to one of more different predicates.
If the primary predicate yield too few filtered servers from the {@link #getEligibleServers(List, Object)}
API, it will try the fallback predicates one by one, until the number of filtered servers
exceeds certain number threshold or percentage threshold. 

@author awang
ribbon-loadbalancer/src/main/java/com/netflix/loadbalancer/CompositePredicate.java