public Duration timeLeft() {
        Instant now = clock.instant();
        Duration duration = Duration.between(now, endTime);
        return duration.isNegative() ? Duration.ZERO : duration;
    }
Handles a timeout logic by providing higher level abstraction for asking if there is time left.

@author Ulf Lilleengen
configserver/src/main/java/com/yahoo/vespa/config/server/TimeoutBudget.java