Update time_to_expire when compose is finished
    
    When a compose transitions to "done" or "failed", update the expiration
    time. Since we don't store the time to live for the compose, we have to
    compute it based on start time and current expiration time.
    
    This should prevent composes that took long time to finish from being
    expired right away after finishing.
    
    JIRA: FACTORY-4864