[#68880956] Use upstream openconnect module

Switch to the open source module that this code later evolved into.

Some key points:

- The vpnc dependency is now bundled into the openconnect module itself.
- This version logs to syslog so we no longer need to append our own
  timestamps to the logs.
- Thus I've removed `gawk` from `system_packages` which is no longer needed
  on new jumpbox machines.
- Fixes a bug whereby the daemon wasn't restarted on argument changes. I
  think this prevented the timestamp fix going out to some PP environments.
- I haven't included a version in `Puppetfile` because it is already pinned
  by `Puppetfile.lock`.

Depends on gds/pp-deployment#206 for new hiera key names.

---

This is difficult/impossible to test in Vagrant because the routes provided by the VPN conflict with the routes you'd normally use to SSH into the VM. So we should test that the following still works from `jumpbox-1` once deployed to preview:
```
dcarley@jumpbox-1:~$ nc -v github.gds 22
Connection to github.gds 22 port [tcp/ssh] succeeded!
SSH-2.0-OpenSSH_5.8p1 Debian-1ubuntu3+github2
```