func mustGetMetadata(key string) []byte {
	b, err := getMetadata(key)
	if err != nil {
		log.Fatalf("Metadata fetch failed: %v", err)
	}
	return b
}
TODO(dsymonds): Do we need to support default values, like Python?
package internal
import (
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"net/url"
)
const (
	metadataHost = "metadata"
	metadataPath = "/computeMetadata/v1/"
)
var (
	metadataRequestHeaders = http.Header{
		"Metadata-Flavor": []string{"Google"},
	}
)