Bug 994819 - [Cost Control] invoke passed callbacks when everything is ready. r=salva

1) apps/costcontrol/js/config/config_manager.js, function
requestSettings, callback may be invoked while a companion
asyncStorage.setItem() call is on going.

2) apps/costcontrol/js/config/config_manager.js, function setOption,
callback may be invoked while a companion requestSettings() call is on
going.

3) apps/costcontrol/js/message_handler.js, function _onNetworkAlarm,
function closeIfProceeds may be invoked while a companion
ConfigManager.setOption() call is on going.
Merge pull request #18908 from vicamo/bugzilla/994819/cost-control-racing-conditions

Bug 994819 - [Cost Control] invoke passed callbacks when everything is ready. r=salva, f=cyang