Merge lp://staging/~ltrager/maas-images/kernels into lp://staging/maas-images

Add support for the new kernel naming format. While the new kernel metapackages haven't been published yet this publishes the existing linux-generic, and linux-image-lowlatency-lts-xenial images using the hwe-16.04 and hwe-16.04-lowlatency names. As the new kernels become available I'll add the hwe-16.04-edge, hwe-16.04-lowlatency-edge, hwe-rolling, hwe-rolling-edge, hwe-rolling-lowlatency, and hwe-rolling-lowlatency-edge kernels. Precise and Trusty still use the old names.

Because the V2 stream can't use the new kernel names I had to create a new config file. As the new kernel names a much longer then the old names I converted the yaml arrays from using [] to newlines with -. I only did this for Xenial and Yakkety as they are the only releases that use the new kernels. If we want to make the config uniform I can do the same for Precise and Trusty. I also converted the --squash flag into a config option.