docker/docker_client.go
func (c *dockerClient) doHTTP(req *http.Request) (*http.Response, error) {
	tr := tlsclientconfig.NewTransport()
	tr.TLSClientConfig = c.tlsClientConfig
	httpClient := &http.Client{Transport: tr}
	return httpClient.Do(req)
}
func (c *dockerClient) doHTTP(req *http.Request) (*http.Response, error) {
	tr := tlsclientconfig.NewTransport()
	tr.TLSClientConfig = c.tlsClientConfig
	httpClient := &http.Client{Transport: tr}
	return httpClient.Do(req)
}
// doHttp uses the clients internal TLS configuration for doing the
// provided HTTP request.  It returns the response and an error on failure.