We've been moving away from config fields expecting file paths that
Terraform will load, instead prefering fields that expect file contents,
leaning on `file()` to do loading from a path.
This helps with consistency and also flexibility - since this makes it
easier to shift sensitive files into environment variables.
Here we add a little helper package to manage the transitional period
for these fields where we support both behaviors.
Also included is the first of several fields being shifted over - SSH
private keys in provisioner connection config.
We're moving to new field names so the behavior is more intuitive, so
instead of `key_file` it's `private_key` now.
Additional field shifts will be included in follow up PRs so they can be
reviewed and discussed individually.
* adds `bastion_*` fields to `connection` which add configuration for a
bastion host
* if `bastion_host` is set, connect to that host first, then jump
through it to make the SSH connection to `host`
* enables SSH Agent forwarding by default
This is needed as preperation for adding WinRM support. There is still
one error in the tests which needs another look, but other than that it
seems like were now ready to start working on the WinRM part…
James Bardin