Add HandlerExecutor & BT to modules-utils For Mainline Project, modules needs to depend on some specific files. modules-utils regroup stand-alone library for such use. This cl is adding * BackgroundThread * BackgroundThreadTest * HandlerExecutor Test has been refactored to be more futur-proof. Bug: 198418216 Tag: #refactor Test: atest ModulesUtilsTests Change-Id: Ie82753719f22d03f1678e4b4e1c550b0dc050bd6