Add the init_stage module to provide synchronous communication between
user mode processes and init process.
init stage0-------1fork----> key app
|2 |3
(listen)<---------4--------- (notify)
|5
init stage1-------6fork----> other app
Close #I3OTSU
Change-Id: Idec84e90f739475e98347a6a681a6953862b0928