BUG=670
TEST=Adds kernel_image_test which tests the new functions.
The kernel image verification pretty much exactly mirror the already existing firmware image verification functions except with a few different/additional fields in a signed kernel image. The firmware signing key is the root key equivalent for kernel images.
This CL also moves the image verification tests to a different script. There's some additional cleanup of the code that I will be submitting separately after this and another pending patches get LGTMed and land.
Review URL: http://codereview.chromium.org/660161
