ARM64 EC2 AMI builds: breaking at grub-install

[jsleeio]

I've been working on this with the goal of building ARM64 AMIs for Kubernetes on AWS — on Debian Stretch. I'm also working on adding ARM64 support to Imagebuilder as part of this.

I'm currently stuck at grub-install; it seems that /boot/efi is missing. How do the official Debian AMIs for ARM64 get built? Given the modifications I've had to make to get this far, it feels like they aren't using bootstrap-vz at all... I see, apparently they use FAI now. Maybe I'd be better off looking at that...

My branch of bootstrap-vz is here: https://github.com/jsleeio/bootstrap-vz/tree/arm64-support

• added support for installing ARM64 kernel and kernel headers
• install ARM64 GRUB packages instead of grub-pc
• ARM64 on AWS requires NVMe, so I've merged @john-pierce's work (NVMe support for ec2 provider #486) into my branch