def add_keys(*additional_keys)
      additional_keys = additional_keys.flatten.compact
      @opts[:keys] ||= []
      @opts[:keys] += additional_keys
      @opts[:keys].uniq!
      @boxes.each do |box|
        box.add_keys *additional_keys
      end
      self
    end
def add_keys(*additional_keys)
      additional_keys = additional_keys.flatten.compact
      @opts[:keys] ||= []
      @opts[:keys] += additional_keys
      @opts[:keys].uniq!
      @boxes.each do |box|
        box.add_keys *additional_keys
      end
      self
    end
Add one or more private keys to each box. Also stores key paths
 in the set so when new boxes are added they will get the same keys,
 * +additional_keys+ is a list of file paths to private keys
 Returns the instance of Rye::Set