Makes StepDownload's TargetPath customizable.

I exposed TargetPath as a config file option "target_path". I don't like
the name, but it follows the naming convention. The purpose of TargetPath
stands unmodified, and it enables a fair amount of customization.

builder/parallels/iso/builder.go

@@ -46,6 +46,7 @@ type Config struct {
 	ISOChecksumType    string   `mapstructure:"iso_checksum_type"`
 	ISOUrls            []string `mapstructure:"iso_urls"`
 	VMName             string   `mapstructure:"vm_name"`
+	TargetPath         string   `mapstructure:"target_path"`
 
 	RawSingleISOUrl string `mapstructure:"iso_url"`
 
@@ -218,6 +219,7 @@ func (b *Builder) Run(ui packer.Ui, hook packer.Hook, cache packer.Cache) (packe
 			Description:  "ISO",
 			ResultKey:    "iso_path",
 			Url:          b.config.ISOUrls,
+			TargetPath:   b.config.TargetPath,
 		},
 		&parallelscommon.StepOutputDir{
 			Force: b.config.PackerForce,

builder/qemu/builder.go

@@ -105,6 +105,7 @@ type Config struct {
 	ShutdownCommand string     `mapstructure:"shutdown_command"`
 	SSHHostPortMin  uint       `mapstructure:"ssh_host_port_min"`
 	SSHHostPortMax  uint       `mapstructure:"ssh_host_port_max"`
+	TargetPath      string     `mapstructure:"target_path"`
 	VNCPortMin      uint       `mapstructure:"vnc_port_min"`
 	VNCPortMax      uint       `mapstructure:"vnc_port_max"`
 	VMName          string     `mapstructure:"vm_name"`
@@ -384,6 +385,7 @@ func (b *Builder) Run(ui packer.Ui, hook packer.Hook, cache packer.Cache) (packe
 			Description:  "ISO",
 			ResultKey:    "iso_path",
 			Url:          b.config.ISOUrls,
+			TargetPath:   b.config.TargetPath,
 		},
 		new(stepPrepareOutputDir),
 		&common.StepCreateFloppy{

builder/virtualbox/iso/builder.go

@@ -49,6 +49,7 @@ type Config struct {
 	ISOChecksumType      string   `mapstructure:"iso_checksum_type"`
 	ISOInterface         string   `mapstructure:"iso_interface"`
 	ISOUrls              []string `mapstructure:"iso_urls"`
+	TargetPath           string   `mapstructure:"target_path"`
 	VMName               string   `mapstructure:"vm_name"`
 
 	RawSingleISOUrl string `mapstructure:"iso_url"`
@@ -234,6 +235,7 @@ func (b *Builder) Run(ui packer.Ui, hook packer.Hook, cache packer.Cache) (packe
 			ResultKey:    "iso_path",
 			Url:          b.config.ISOUrls,
 			Extension:    "iso",
+			TargetPath:   b.config.TargetPath,
 		},
 		&vboxcommon.StepOutputDir{
 			Force: b.config.PackerForce,

builder/vmware/iso/builder.go

@@ -49,6 +49,7 @@ type Config struct {
 	VMName              string   `mapstructure:"vm_name"`
 	BootCommand         []string `mapstructure:"boot_command"`
 	SkipCompaction      bool     `mapstructure:"skip_compaction"`
+	TargetPath          string   `mapstructure:"target_path"`
 	VMXTemplatePath     string   `mapstructure:"vmx_template_path"`
 	VMXDiskTemplatePath string   `mapstructure:"vmx_disk_template_path"`
 
@@ -260,6 +261,7 @@ func (b *Builder) Run(ui packer.Ui, hook packer.Hook, cache packer.Cache) (packe
 			Description:  "ISO",
 			ResultKey:    "iso_path",
 			Url:          b.config.ISOUrls,
+			TargetPath:   b.config.TargetPath,
 		},
 		&vmwcommon.StepOutputDir{
 			Force: b.config.PackerForce,

common/packer_config.go

@@ -4,9 +4,10 @@ package common
 // are sent by packer, properly tagged already so mapstructure can load
 // them. Embed this structure into your configuration class to get it.
 type PackerConfig struct {
-	PackerBuildName   string            `mapstructure:"packer_build_name"`
-	PackerBuilderType string            `mapstructure:"packer_builder_type"`
-	PackerDebug       bool              `mapstructure:"packer_debug"`
-	PackerForce       bool              `mapstructure:"packer_force"`
-	PackerUserVars    map[string]string `mapstructure:"packer_user_variables"`
+	PackerBuildName     string            `mapstructure:"packer_build_name"`
+	PackerBuilderType   string            `mapstructure:"packer_builder_type"`
+	PackerDebug         bool              `mapstructure:"packer_debug"`
+	PackerForce         bool              `mapstructure:"packer_force"`
+	PackerUserVars      map[string]string `mapstructure:"packer_user_variables"`
+	PackerIsoTargetPath string            `mapstructure:"packer_iso_target_path"`
 }

common/step_download.go

@@ -71,7 +71,7 @@ func (s *StepDownload) Run(state multistep.StateBag) multistep.StepAction {
 			// if we force a certain extension we hash the URL and add
 			// the extension to force it.
 			cacheKey := url
-			if s.Extension != "" {
+			if s.Extension != "" { //HERE.
 				hash := sha1.Sum([]byte(url))
 				cacheKey = fmt.Sprintf(
 					"%s.%s", hex.EncodeToString(hash[:]), s.Extension)