HTTP client transport replacement makes docker unreachable with the docker client.

[denismakogon]

If i would do something like:

client, err := docker.NewClientFromEnv()

and then:

	t := &http.Transport{
		Dial: (&net.Dialer{
			Timeout:   10 * time.Second,
			KeepAlive: 1 * time.Minute,
		}).Dial,
		TLSClientConfig: &tls.Config{
			ClientSessionCache: tls.NewLRUClientSessionCache(8192),
		},
		TLSHandshakeTimeout:   10 * time.Second,
		MaxIdleConnsPerHost:   512,
		Proxy:                 http.ProxyFromEnvironment,
		MaxIdleConns:          512,
		IdleConnTimeout:       90 * time.Second,
		ExpectContinueTimeout: 1 * time.Second,
	}
       client.HTTPClient = &http.Client{Transport: t}

would lead to the following error:

Get http://unix.sock/_ping: dial tcp: lookup unix.sock: no such host

So, there has to be the way to replace HTTP client.