Use audio element to play audio instead of the Audio API.

Audio API doesn't support AMR file on Firefox OS device, so I changed the implementation to use audio tag.
The new implementation fixes bug #758 to make `AudioPlayer::getMediaTime` returns the duration when the audio ends.

It also makes improvement on TestAudioPlayer to avoid intermittent test failure.
The audio playing after resume or replay is buggy and test is quite unreliable, so I have to avoid such test before [gecko bug 816041]( https://bugzilla.mozilla.org/show_bug.cgi?id=816041) fixed.