[incubator/openvpn] Can't log in in VPN client

Hi,

I've managed to install the chart and make it work with the latest letsencrypt (had to create RBAC stuff and set the letsencrypt_ca to `https://acme-v02.api.letsencrypt.org/directory` to avoid an "ACME V1" error), but I can't seem to log in in my VPN client.

The certificate is created as `simon` even though my github username is `fredsted`, not sure if that has anything to do with it.

Here's some output from the openvpn pod:

```AUTH-PAM: BACKGROUND: user 'fredsted' failed to authenticate: User not known to the underlying authentication module
Fri Jan 24 13:50:30 2020 172.21.48.88:7254 PLUGIN_CALL: POST /usr/lib/openvpn/plugins/openvpn-plugin-auth-pam.so/PLUGIN_AUTH_USER_PASS_VERIFY status=1
Fri Jan 24 13:50:30 2020 172.21.48.88:7254 PLUGIN_CALL: plugin function PLUGIN_AUTH_USER_PASS_VERIFY failed with status 1: /usr/lib/openvpn/plugins/openvpn-plugin-auth-pam.so
Fri Jan 24 13:50:30 2020 172.21.48.88:7254 TLS Auth Error: Auth Username/Password verification failed for peer
Fri Jan 24 13:50:30 2020 172.21.48.88:7254 WARNING: cipher with small block size in use, reducing reneg-bytes to 64MB to mitigate SWEET32 attacks.
Fri Jan 24 13:50:30 2020 172.21.48.88:7254 Control Channel: TLSv1.2, cipher TLSv1/SSLv3 DHE-RSA-AES256-GCM-SHA384, 2048 bit RSA
Fri Jan 24 13:50:30 2020 172.21.48.88:7254 [simon] Peer Connection Initiated with [AF_INET]172.21.48.88:7254
```

I'm using Google Authenticator for Github, so I've tried several combinations of simon/fredsted and with/without my Google Authenticator code.

I can also see that the link to "Github PAM" does not work, so I can't investigate that part further. https://github.com/cloudposse/github-pam

Is it possible to just delete the password authentication from the VPN? I can make do with the oauth sign-in-to-download-vpn-config part.

@alebabai @osterman