add test-kitchen .kitchen.yml directives for FreeBSD

Unfortunately, there seems to be a Vagrant bug that causes FreeBSD boxes to fail on first startup:

```text
       ==> default: Waiting for machine to boot. This may take a few minutes...
           default: SSH address: 127.0.0.1:2222
           default: SSH username: vagrant
           default: SSH auth method: private key
           default: Warning: Connection timeout. Retrying...
           default: Warning: Connection timeout. Retrying...
       The configured shell (config.ssh.shell) is invalid and unable
       to properly execute commands. The most common cause for this is
       using a shell that is unavailable on the system. Please verify
       you're using the full path to the shell and that the shell is
       executable by the SSH user.
```

I haven't dug into it further, because it always works the second time. Annoying as it is, we should still have a harness for FreeBSD here.