Adjust some parameters for VP9 tests.

Needed for the next/upcoming libvpx roll.

BUG=

TBR=stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/32679004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7821 4adac7df-926f-26a2-2b94-8c16560cd09d