upower template: Add defined DisplayDevice properties

See http://cgit.freedesktop.org/upower/tree/src/org.freedesktop.UPower.xml

https://launchpad.net/bugs/1245955
upower template: Add SetupDisplayDevice() method on the mock interface to conveniently configure all defined properties of the DisplayDevice. Only available when using the 1.0 API. (LP: #1245955)
release 0.8
Fix test failure if the "upower" tool is not installed.