def running?(pos=nil)
      group = pos.nil? ? list : [get(pos)].compact
      return false if group.nil? || group.empty?
      group.collect! { |m| m.instance_running? }
      !group.member?(false)
    end
def running?(pos=nil)
      group = pos.nil? ? list : [get(pos)].compact
      return false if group.nil? || group.empty?
      group.collect! { |m| m.instance_running? }
      !group.member?(false)
    end
Returns true if all machines in the group are running instances