Bug 1083129 - [System][Music] send pause command to music app when headsets are disconnected

Conflicts:

	apps/system/test/unit/media_playback_test.js
Merge pull request #25682 from dominickuo/v2.1-bug-1083129

Bug 1083129 - [System][Music] send pause command to music app when headsets are disconnected, r=jimporter