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