Return errors from Openvpn layer

[Waldz]

session := NewSession(&fmtLogger{})
session.Start("", Credentials{})
err := session.Wait()

Problems:

• Error is not informative, it's always the same

err = "openvpn3 init failed"

• Detailed error is only in logs:

eval config error: option_error: remote option not specified

• And in Openvpn layer swallows it:

build/core/adapter/library.cpp:
try {
  if (eval.error) {
    OPENVPN_THROW_EXCEPTION("eval config error: " << eval.message);
  }
} catch (const std::exception &e) {
  callbacks.logCallback(callbacks.usrData, (char *)(e.what()));
}

[tadovas]

Actually it doesn't swallow, but reports it through Log callback - unfortunatelly as simple string