Bug 979134: refactor head.js a little bit.
Bug 979134: convert test_mobile_networks.js to Promise.
Bug 979134: convert test_mobile_voice_state.js to Promise.
Bug 979134: convert test_mobile_data_state.js to Promise.
Bug 979134: convert test_mobile_voice_location.js to Promise.
Bug 979134: convert test_mobile_data_location.js to Promise.
Bug 979134: convert test_mobile_operator_names.js to Promise.