Remote Site should check version of Auth server not Proxy server

[rosstimothy]

When creating a remote site we check the version of the remote cluster to determine how to initialize the cache to account for different resources being emitted based on different version. However the check is only checking the version of the proxy and not auth. This can lead to issue if the auth server and proxy server in the remote cluster are not on the same version. In such a scenario it is possible that the remote site cache will indefinitely be unhealthy.

teleport/lib/reversetunnel/srv.go

Lines 1152 to 1179 in 8c887bb

	func sendVersionRequest(ctx context.Context, sconn ssh.Conn) (string, error) {
	errorCh := make(chan error, 1)
	versionCh := make(chan string, 1)
	go func() {
	ok, payload, err := sconn.SendRequest(versionRequest, true, nil)
	if err != nil {
	errorCh <- err
	return
	}
	if !ok {
	errorCh <- trace.BadParameter("no response to %v request", versionRequest)
	return
	}
	versionCh <- string(payload)
	}()
	select {
	case ver := <-versionCh:
	return ver, nil
	case err := <-errorCh:
	return "", trace.Wrap(err)
	case <-time.After(defaults.WaitCopyTimeout):
	return "", trace.BadParameter("timeout waiting for version")
	case <-ctx.Done():
	return "", ctx.Err()
	}
	}