feat(fetch): stub out fetch command

cmd/helm/fetch.go

+package main
+
+import (
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+
+	"github.com/spf13/cobra"
+)
+
+func init() {
+	RootCommand.AddCommand(fetchCmd)
+}
+
+var fetchCmd = &cobra.Command{
+	Use:   "fetch",
+	Short: "Download a chart from a repository and unpack it in local directory.",
+	Long:  "",
+	RunE:  Fetch,
+}
+
+func Fetch(cmd *cobra.Command, args []string) error {
+	// parse args
+	// get download url
+	// call download url
+	out, err := os.Create("nginx-2.0.0.tgz")
+	if err != nil {
+		return err
+	}
+	defer out.Close()
+	resp, err := http.Get("http://localhost:8879/charts/nginx-2.0.0.tgz")
+	fmt.Println("after req")
+	// unpack file
+	if err != nil {
+		return err
+	}
+
+	defer resp.Body.Close()
+
+	_, err = io.Copy(out, resp.Body)
+	if err != nil {
+		return err
+	}
+	return nil
+}