builder/*: Adhere to the new interface

builder/amazonebs/builder.go

@@ -44,11 +44,15 @@ type Builder struct {
 	runner multistep.Runner
 }
 
-func (b *Builder) Prepare(raw interface{}) error {
+func (b *Builder) Prepare(raws ...interface{}) error {
+	var err error
+
+	for _, raw := range raws {
 		err := mapstructure.Decode(raw, &b.config)
 		if err != nil {
 			return err
 		}
+	}
 
 	if b.config.SSHPort == 0 {
 		b.config.SSHPort = 22

builder/virtualbox/builder.go

@@ -47,11 +47,15 @@ type config struct {
 	RawSSHWaitTimeout  string `mapstructure:"ssh_wait_timeout"`
 }
 
-func (b *Builder) Prepare(raw interface{}) error {
+func (b *Builder) Prepare(raws ...interface{}) error {
 	var err error
-	if err := mapstructure.Decode(raw, &b.config); err != nil {
+
+	for _, raw := range raws {
+		err := mapstructure.Decode(raw, &b.config)
+		if err != nil {
 			return err
 		}
+	}
 
 	if b.config.GuestOSType == "" {
 		b.config.GuestOSType = "Other"

builder/vmware/builder.go

@@ -49,10 +49,13 @@ type config struct {
 	RawSSHWaitTimeout  string `mapstructure:"ssh_wait_timeout"`
 }
 
-func (b *Builder) Prepare(raw interface{}) error {
-	if err := mapstructure.Decode(raw, &b.config); err != nil {
+func (b *Builder) Prepare(raws ...interface{}) error {
+	for _, raw := range raws {
+		err := mapstructure.Decode(raw, &b.config)
+		if err != nil {
 			return err
 		}
+	}
 
 	if b.config.DiskName == "" {
 		b.config.DiskName = "disk"