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/user.go

@@ -0,0 +1,53 @@
+package packngo
+
+const userBasePath = "/users"
+
+// UserService interface defines available user methods
+type UserService interface {
+	Get(string) (*User, *Response, error)
+}
+
+// User represents a Packet user
+type User struct {
+	ID          string  `json:"id"`
+	FirstName   string  `json:"first_name,omitempty"`
+	LastName    string  `json:"last_name,omitempty"`
+	FullName    string  `json:"full_name,omitempty"`
+	Email       string  `json:"email,omitempty"`
+	TwoFactor   string  `json:"two_factor_auth,omitempty"`
+	AvatarURL   string  `json:"avatar_url,omitempty"`
+	Facebook    string  `json:"twitter,omitempty"`
+	Twitter     string  `json:"facebook,omitempty"`
+	LinkedIn    string  `json:"linkedin,omitempty"`
+	Created     string  `json:"created_at,omitempty"`
+	Updated     string  `json:"updated_at,omitempty"`
+	TimeZone    string  `json:"timezone,omitempty"`
+	Emails      []Email `json:"email,omitempty"`
+	PhoneNumber string  `json:"phone_number,omitempty"`
+	URL         string  `json:"href,omitempty"`
+}
+
+func (u User) String() string {
+	return Stringify(u)
+}
+
+// UserServiceOp implements UserService
+type UserServiceOp struct {
+	client *Client
+}
+
+// Get method gets a user by userID
+func (s *UserServiceOp) Get(userID string) (*User, *Response, error) {
+	req, err := s.client.NewRequest("GET", userBasePath, nil)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	user := new(User)
+	resp, err := s.client.Do(req, user)
+	if err != nil {
+		return nil, resp, err
+	}
+
+	return user, resp, err
+}