Free up space on the cloud-images.ubuntu.com boxes by removing the kerne...

...l 3.2 headers (only kernel 3.8 is actually installed.)

This is such a simple change that I'll merge it without discussing. I have tested it successfully. There is a safeguard (if kernel 3.2 is installed, do not remove the kernel 3.2 headers.)

Note that this logic is not specific to duckpan, it's specific to the cloud-images.ubuntu.com boxes. If there turn out to be a lot more fixes/optimizations needed for the boxes, I'll put them in a separate recipe, or a separate cookbook.