add a test vector with frame parallel mode enabled

vp90-2-07-frame_parallel.webm:
vpxenc stefan_sif.y4m \
  --codec=vp9 -p 2 \
  --frame-parallel=1 \
  --limit=10 \
  --auto-alt-ref=1 \
  --lag-in-frames=5

Change-Id: I7381a69aaaec238b309169a51b34cb6bf29a9c50