Allow specifying project for source images in GCE

Within GCE, images may be shared across projects. Prior to this
commit, there was no way to inform the GCE builder that a source
image belonged to a specific project. This adds an optional
'source_image_project_id' key to the GCE builder config.

builder/googlecompute/config.go

@@ -29,6 +29,7 @@ type Config struct {
 	PrivateKeyFile       string            `mapstructure:"private_key_file"`
 	ProjectId            string            `mapstructure:"project_id"`
 	SourceImage          string            `mapstructure:"source_image"`
+	SourceImageProjectId string            `mapstructure:"source_image_project_id"`
 	SSHUsername          string            `mapstructure:"ssh_username"`
 	SSHPort              uint              `mapstructure:"ssh_port"`
 	RawSSHTimeout        string            `mapstructure:"ssh_timeout"`
@@ -114,6 +115,7 @@ func NewConfig(raws ...interface{}) (*Config, []string, error) {
 		"private_key_file":        &c.PrivateKeyFile,
 		"project_id":              &c.ProjectId,
 		"source_image":            &c.SourceImage,
+		"source_image_project_id": &c.SourceImageProjectId,
 		"ssh_username":            &c.SSHUsername,
 		"ssh_timeout":             &c.RawSSHTimeout,
 		"state_timeout":           &c.RawStateTimeout,

builder/googlecompute/driver.go

@@ -23,10 +23,15 @@ type Driver interface {
 	WaitForInstance(state, zone, name string) <-chan error
 }
 
+type Image struct {
+	Name      string
+	ProjectId string
+}
+
 type InstanceConfig struct {
 	Description string
 	DiskSizeGb  int64
-	Image       string
+	Image       Image
 	MachineType string
 	Metadata    map[string]string
 	Name        string

builder/googlecompute/driver_gce.go

@@ -134,7 +134,7 @@ func (d *driverGCE) RunInstance(c *InstanceConfig) (<-chan error, error) {
 	}
 
 	// Get the image
-	d.ui.Message(fmt.Sprintf("Loading image: %s", c.Image))
+	d.ui.Message(fmt.Sprintf("Loading image: %s in project %s", c.Image.Name, c.Image.ProjectId))
 	image, err := d.getImage(c.Image)
 	if err != nil {
 		return nil, err
@@ -229,17 +229,17 @@ func (d *driverGCE) WaitForInstance(state, zone, name string) <-chan error {
 	return errCh
 }
 
-func (d *driverGCE) getImage(name string) (image *compute.Image, err error) {
-	projects := []string{d.projectId, "centos-cloud", "coreos-cloud", "debian-cloud", "google-containers", "opensuse-cloud", "rhel-cloud", "suse-cloud", "windows-cloud"}
+func (d *driverGCE) getImage(img Image) (image *compute.Image, err error) {
+	projects := []string{img.ProjectId, "centos-cloud", "coreos-cloud", "debian-cloud", "google-containers", "opensuse-cloud", "rhel-cloud", "suse-cloud", "windows-cloud"}
 	for _, project := range projects {
-		image, err = d.service.Images.Get(project, name).Do()
+		image, err = d.service.Images.Get(project, img.Name).Do()
 		if err == nil && image != nil && image.SelfLink != "" {
 			return
 		}
 		image = nil
 	}
 
-	err = fmt.Errorf("Image %s could not be found in any of these projects: %s", name, projects)
+	err = fmt.Errorf("Image %s could not be found in any of these projects: %s", img.Name, projects)
 	return
 }
 

builder/googlecompute/step_create_instance.go

@@ -16,6 +16,14 @@ type StepCreateInstance struct {
 	instanceName string
 }
 
+func (config *Config) getImage() (Image) {
+	project := config.ProjectId
+	if config.SourceImageProjectId != "" {
+		project = config.SourceImageProjectId
+	}
+	return Image{Name: config.SourceImage, ProjectId: project}
+}
+
 // Run executes the Packer build step that creates a GCE instance.
 func (s *StepCreateInstance) Run(state multistep.StateBag) multistep.StepAction {
 	config := state.Get("config").(*Config)
@@ -29,7 +37,7 @@ func (s *StepCreateInstance) Run(state multistep.StateBag) multistep.StepAction
 	errCh, err := driver.RunInstance(&InstanceConfig{
 		Description: "New instance created by Packer",
 		DiskSizeGb:  config.DiskSizeGb,
-		Image:       config.SourceImage,
+		Image:       config.getImage(),
 		MachineType: config.MachineType,
 		Metadata: map[string]string{
 			"sshKeys": fmt.Sprintf("%s:%s", config.SSHUsername, sshPublicKey),