Use smaller images in SnapshotComparer spec
Use smaller images in SnapshotComparer spec

Since we iterate over every pixel in these images, we may as well save a
bunch of cycles on every test run by making these images smaller. This
will make the tests run faster and require less energy.

Change-Id: Iafaa9ae87a1903e90d2840ea494c2aadfff29091

kalw/diffux,kalw/diffux,diffux/diffux,diffux/diffux,kalw/diffux,diffux/diffux