Log the relative time remaining for this est_complete datetime object.

def log_est_complete(est_complete):
    """
    Log the relative time remaining for this est_complete datetime object.
    """
    if not est_complete:
        print('could not determine an estimated completion time')
        return
    remaining = est_complete - datetime.utcnow()
    message = 'this task should be complete in %s'
    if remaining.total_seconds() < 0:
        message = 'this task exceeds estimate by %s'
    log_delta(message, remaining)