enable grunt to receive coverage raw data from phantomjs

unit test coverage is important as long as running tests. by use `grunt-contrib-jasmine` together with `grunt-istanbul` (or other istanbul like plugin), the generated coverage data needs to be passed from phantomjs to grunt for next step processing to make a report, means fully automated the *instrument -> running test -> make report* flow.

This change introduce a new jasmine event to pass that data. 
Test for the change also added.