navigator.getBattery() test

According to Battery Status API CR on 09 December 2014, pepole who want
to use Battery API should use getBattery method. But existing tests are
based on WD and don't use getBattery method. So, I try to test this
method.
delete extra space
Merge pull request #1465 from YuichiNukiyama/yuchinukiyama/battertest

navigator.getBattery() test