power: refreshUpower via listen prop changed

delete freedesktop upower signals: Changed
add testing codes for dbus interface

tower: https://tower.im/projects/8f19f0bf0e754f0b82ef2c24bc230973/todos/faa09bca6b2843b7aceb34be415c3442/

Change-Id: Ie8cfb4f5de1af705d6f927e0e7e5124e21aee271