Support ARM instance types

This depends on the template-updates in #67

The magic numbers for console speed, nvme timeout, and block offset all come from the Amazon Linux and Ubuntu AMIs.

We'll want to remove the install_updated_aarch64_kernel function once the upstream virt kernel has the ena patches. This should be within the next day or so for edge and in the 3.12 release. I'll push some changes to this to integrate the test profile into the alpine one but wanted to get this out for review as soon as it was cleaned up.