Encode OpenVPN password + OTP in tunnel rather than in the app.
Encoding them upfront in the app ends up persisting the profile with the
combined password. Update the library with a new OTP field in
OpenVPN.Credentials, so that the password encoding is performed [on the
fly in the
tunnel](https://github.com/passepartoutvpn/passepartoutkit-source/pull/398).
Similar to how provider modules are generated.
This is likely a regression caused by migrating to NEProfileRepository,
because starting a connection causes the profile to be saved to NE with
the encoded password. Later, the profile is restored from NE and
therefore contains the encoded password.
bb8c760278