Update agl-service-windowmanager-2017 SRCREV

Update agl-service-windowmanager-2017 SRCREV

Update agl-service-windowmanager-2017 SRCREV to
  <c392fff74872af6d4f165ff3f854d19f390ec0ee>
Related commit: https://gerrit.automotivelinux.org/gerrit/#/c/11819/

Following commits are added:
  c392fff Remove and replace the comments
  0b1d9ca Add the fail-safe process for the configuration file
  2b97202 Fix the error log on windowmanager initialization
  7879eaa Update the application guide
  fe5ec2c Merge "Add an another example for layout configuration"
  3810b9b Add an another example for layout configuration
   create mode 100644 layers.json.split
  3357a19 Update application guide

Change-Id: Ie39087431922b3d822d24efd4fe0fe3a74fe93da
Signed-off-by: zheng_wenlong <wenlong_zheng@nexty-ele.com>
Signed-off-by: Tadao Tanikawa <tanikawa.tadao@jp.panasonic.com>