Add moby run packet to boot on baremetal Packet.net hosts

This uses the Packet.net API and iPXE to boot a Moby host.
There are several enhancements coming soon, such as SSH key
customisation, but this PR is sufficient to boot a host and
then use the web interface to get console access.

The user must currently upload the built artefacts to a public
URL and specify it via --base-url, e.g.:
moby run packet --api-key <key> --project-id <id> \
  --base-url http://recoil.org/~avsm/ipxe --hostname test-moby packet

See #1424 #1245 for related issues.

Signed-off-by: Anil Madhavapeddy <anil@docker.com>

vendor/github.com/packethost/packngo/utils.go

@@ -0,0 +1,112 @@
+package packngo
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"reflect"
+)
+
+var timestampType = reflect.TypeOf(Timestamp{})
+
+// Stringify creates a string representation of the provided message
+func Stringify(message interface{}) string {
+	var buf bytes.Buffer
+	v := reflect.ValueOf(message)
+	stringifyValue(&buf, v)
+	return buf.String()
+}
+
+// String allocates a new string value to store v and returns a pointer to it
+func String(v string) *string {
+	p := new(string)
+	*p = v
+	return p
+}
+
+// Int allocates a new int32 value to store v and returns a pointer to it, but unlike Int32 its argument value is an int.
+func Int(v int) *int {
+	p := new(int)
+	*p = v
+	return p
+}
+
+// Bool allocates a new bool value to store v and returns a pointer to it.
+func Bool(v bool) *bool {
+	p := new(bool)
+	*p = v
+	return p
+}
+
+// StreamToString converts a reader to a string
+func StreamToString(stream io.Reader) string {
+	buf := new(bytes.Buffer)
+	buf.ReadFrom(stream)
+	return buf.String()
+}
+
+// stringifyValue was graciously cargoculted from the goprotubuf library
+func stringifyValue(w io.Writer, val reflect.Value) {
+	if val.Kind() == reflect.Ptr && val.IsNil() {
+		w.Write([]byte("<nil>"))
+		return
+	}
+
+	v := reflect.Indirect(val)
+
+	switch v.Kind() {
+	case reflect.String:
+		fmt.Fprintf(w, `"%s"`, v)
+	case reflect.Slice:
+		w.Write([]byte{'['})
+		for i := 0; i < v.Len(); i++ {
+			if i > 0 {
+				w.Write([]byte{' '})
+			}
+
+			stringifyValue(w, v.Index(i))
+		}
+
+		w.Write([]byte{']'})
+		return
+	case reflect.Struct:
+		if v.Type().Name() != "" {
+			w.Write([]byte(v.Type().String()))
+		}
+
+		// special handling of Timestamp values
+		if v.Type() == timestampType {
+			fmt.Fprintf(w, "{%s}", v.Interface())
+			return
+		}
+
+		w.Write([]byte{'{'})
+
+		var sep bool
+		for i := 0; i < v.NumField(); i++ {
+			fv := v.Field(i)
+			if fv.Kind() == reflect.Ptr && fv.IsNil() {
+				continue
+			}
+			if fv.Kind() == reflect.Slice && fv.IsNil() {
+				continue
+			}
+
+			if sep {
+				w.Write([]byte(", "))
+			} else {
+				sep = true
+			}
+
+			w.Write([]byte(v.Type().Field(i).Name))
+			w.Write([]byte{':'})
+			stringifyValue(w, fv)
+		}
+
+		w.Write([]byte{'}'})
+	default:
+		if v.CanInterface() {
+			fmt.Fprint(w, v.Interface())
+		}
+	}
+}