Provide a shortcut for proxying minikube

go/fake-http/README.md

`minikube start`.
```
# shortcut for the cmdline below: fake-http -proxy-minikube
$ fake-http -proxy-url=https://$(minikube ip):8443 -proxy-client-cert ~/.minikube/client.crt -proxy-client-key ~/.minikube/client.key
2018/06/09 13:21:19 Listening on http://localhost:8080
2018/06/09 13:21:19 See http://localhost:8080/_help

go/fake-http/fake-http.go

	"net/http"
	"net/http/httputil"
	"net/url"
	"os"
	"os/exec"
	"path"
	"strings"
	"gopkg.in/yaml.v2"
	proxyURL        string
	proxyClientCert string
	proxyClientKey  string
	proxyMinikube bool
}
func init() {
	flag.StringVar(&flags.proxyURL, "proxy-url", "", "Proxy requests to this URL")
	flag.StringVar(&flags.proxyClientCert, "proxy-client-cert", "", "Client certificate to use when connecting to proxy")
	flag.StringVar(&flags.proxyClientKey, "proxy-client-key", "", "Client key to use when connecting to proxy")
	flag.BoolVar(&flags.proxyMinikube, "proxy-minikube", false, "Shortcut for -proxy-url=https://$(minikube ip):8443 -proxy-client-cert ~/.minikube/client.crt -proxy-client-key ~/.minikube/client.key")
}
var responses = []Response{}
func main() {
	flag.Parse()
	if flags.proxyMinikube {
		err := proxyMinikube()
		if err != nil {
			log.Fatalf("Error: Setting up Minikube proxy: %s", err)
		}
	}
	if flag.NArg() == 1 {
		rs, err := loadResponses(flag.Arg(0))
		if err != nil {
	log.Fatal(http.ListenAndServe(flags.addr, nil))
}
func proxyMinikube() error {
	out, err := exec.Command("minikube", "ip").Output()
	if err != nil {
		return err
	}
	flags.proxyURL = fmt.Sprintf("https://%s:8443", strings.TrimSpace(string(out)))
	homeDir := os.Getenv("HOME")
	flags.proxyClientCert = path.Join(homeDir, ".minikube/client.crt")
	flags.proxyClientKey = path.Join(homeDir, ".minikube/client.key")
	return nil
}
func matchResponse(req *http.Request, responses []Response) *Response {
	for _, resp := range responses {
		if req.Method == resp.Method && req.URL.Path == resp.Path {