upgrade machine image for most jobs
upgrade machine image for most jobs

Looks like the host unattended upgrades is interferring with chroot
creation.  Here, we upgrade machine image to one without unattended
upgrades misconfigured, across the board except for the `test-docker`
job.

Docker seems to be misbehaving on that image, and we get some unexpected
cgroups errors, e.g. https://circleci.com/gh/hashicorp/nomad/3854 .

Sample recent failures of `test-exec`:

https://circleci.com/gh/hashicorp/nomad/3633
https://circleci.com/gh/hashicorp/nomad/3696
https://circleci.com/gh/hashicorp/nomad/3714
https://circleci.com/gh/hashicorp/nomad/3764
https://circleci.com/gh/hashicorp/nomad/3770
https://circleci.com/gh/hashicorp/nomad/3834

dvusboy/nomad,hashicorp/nomad,burdandrei/nomad,dvusboy/nomad,burdandrei/nomad,hashicorp/nomad,dvusboy/nomad,dvusboy/nomad,dvusboy/nomad,burdandrei/nomad,burdandrei/nomad,dvusboy/nomad,burdandrei/nomad,hashicorp/nomad,burdandrei/nomad,hashicorp/nomad,hashicorp/nomad,dvusboy/nomad,burdandrei/nomad,hashicorp/nomad