builder/amazon/chroot: use the attached device path

builder/amazon/chroot/builder.go

@@ -63,6 +63,10 @@ func (b *Builder) Prepare(raws ...interface{}) error {
 		b.config.DevicePath = "/dev/sdh"
 	}
 
+	if b.config.AttachedDevicePath == "" {
+		b.config.AttachedDevicePath = "/dev/xvdh"
+	}
+
 	if b.config.MountCommand == "" {
 		b.config.MountCommand = "mount"
 	}

builder/amazon/chroot/step_attach_volume.go

@@ -69,7 +69,7 @@ func (s *StepAttachVolume) Run(state map[string]interface{}) multistep.StepActio
 		return multistep.ActionHalt
 	}
 
-	state["device"] = device
+	state["device"] = config.AttachedDevicePath
 	return multistep.ActionContinue
 }