Sets up a virtual machine image that is bootable on Yandex Cloud.
There are some slightly wonky behaviours still, like cloud-init
apparently putting all keys into root's authorized_keys no matter what
is specified in the metadata, but it does work now.
Change-Id: I57dcb7fcfa6872a28855dc1347f73a6db3c56828
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8496
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>