Merge changes I4874b421,Ibe78b615

* changes:
  [Title] change brightness level setting [Type] Bugfix [Module] Emulator / Display [Priority] Minor [CQ#] [Redmine#] C API - 301 [Problem] [Cause] [Solution] subdividing brightness level from 10 to 24 [TestCase]
  [Title] exit hang problem after using the shell menu. [Type] Bugfix [Module] Emulator / Display [Priority] Major [CQ#] [Redmine#] 3382 [Problem] [Cause] select blocking in qemu_loop_wait function of vl.c at exit time. [Solution] workaround : call qemu_system_shutdown_request explictly [TestCase]