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/facilities.go

@@ -0,0 +1,56 @@
+package packngo
+
+const facilityBasePath = "/facilities"
+
+// FacilityService interface defines available facility methods
+type FacilityService interface {
+	List() ([]Facility, *Response, error)
+}
+
+type facilityRoot struct {
+	Facilities []Facility `json:"facilities"`
+}
+
+// Facility represents a Packet facility
+type Facility struct {
+	ID       string   `json:"id"`
+	Name     string   `json:"name,omitempty"`
+	Code     string   `json:"code,omitempty"`
+	Features []string `json:"features,omitempty"`
+	Address  *Address `json:"address,omitempty"`
+	URL      string   `json:"href,omitempty"`
+}
+
+func (f Facility) String() string {
+	return Stringify(f)
+}
+
+// Address - the physical address of the facility
+type Address struct {
+	ID string `json:"id,omitempty"`
+}
+
+func (a Address) String() string {
+	return Stringify(a)
+}
+
+// FacilityServiceOp implements FacilityService
+type FacilityServiceOp struct {
+	client *Client
+}
+
+// List returns all available Packet facilities
+func (s *FacilityServiceOp) List() ([]Facility, *Response, error) {
+	req, err := s.client.NewRequest("GET", facilityBasePath, nil)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	root := new(facilityRoot)
+	resp, err := s.client.Do(req, root)
+	if err != nil {
+		return nil, resp, err
+	}
+
+	return root.Facilities, resp, err
+}