Add multiple layers test json example.

Add multiple layers test json example.

The example json includes 5 layers: 3 kms cube test layers, and 2 video
layers which is using the argb video file. The layers also are placed with
overlay, and runing separately. This is just a example, and users can add
their multiple layers tests according their requirements with the json
format.

Jira: None.
Test: Use the command "ffmpeg -i ./1080p_29.97fps.mp4 -ss 30 -frames
      100 -f rawvideo -pix_fmt argb test.xrgb" to generate video raw
      file as test resources, and using current multiplelayers.json to
      test if the "testlayers" app can show and run all layers normally.

Signed-off-by: Fan Yugang <yugang.fan@intel.com>