Add tests for Vibration API

These tests shall fulfill the gaps in TODO.txt and in
http://lists.w3.org/Archives/Public/public-device-apis/2014Jul/0059.html
based on the spec at
http://dev.w3.org/2009/dap/vibration/#vibration-interface
Merge pull request #1224 from zqzhang/zqzhang/vibrate

Add tests for Vibration API