Add an Elastic Network Interface (ENI) to each Linux host, on a secondary subnet
we have provisioned in each AZ. Revise security groups as follows:
* Split out client security groups from servers so that we can't have clients
accidentally accessing serf addresses or other unexpected cross-talk.
* Add new security groups for the secondary subnet that only allows
communication within the security group so we can exercise behaviors with
multiple IPs.
This changeset doesn't include any Nomad configuration changes needed to take
advantage of the extra network interface. I'll include those with testing for
PR #16217.
Includes:
* baseline Windows AMI
* initial pass at Terraform configurations
* OpenSSH for Windows
Using OpenSSH is a lot nicer for Nomad developers than winrm would be,
plus it lets us avoid passing around the Windows password in the
clear.
Note that now we're copying up all the provisioning scripts and
configs as a zipped bundle because TF's file provisioner dies in the
middle of pushing up multiple files (whereas `scp -r` works fine).
We're also running all the provisioning scripts inside the userdata by
polling for the zip file to show up (gross!). This is because
`remote-exec` provisioners are failing on Windows with the same symptoms as:
https://github.com/hashicorp/terraform/issues/17728
If we can't fix this, it'll prevent us from having multiple Windows
clients running until TF supports count interpolation in the
`template_file`, which is planned for a later 0.12 release.
