The previous jessie image had a broken cloud-init, which would use an
Ubuntu-specific 'nobootwait' argument when mounting disks. We now
override that in the image.
Fix#22549
Based on the official debian image, with the following changes:
* Switched extlinux -> grub, because we need to change kernel options
to enable the memory cgroup controller, and extlinux is harder and has
reboot problems
* Added packages that would otherwise be installed as part of the boot
(just an optimization)
* Also add the cloud-initramfs-growroot package; with it the root
volume will resize.
* We add panic=10 & oops=panic to kernel options
* We install the packages as per the base image, except we install
awscli from pip, because the repo version is really old.
