add CD-ROM only if not used disk_image, also boot from it only if CD-ROM present

Signed-off-by: Vasiliy Tolstov <v.tolstov@selfip.ru>

builder/qemu/builder.go

@@ -418,6 +418,15 @@ func (b *Builder) Run(ui packer.Ui, hook packer.Hook, cache packer.Cache) (packe
 		return nil, fmt.Errorf("Failed creating Qemu driver: %s", err)
 	}
 
+	steprun := &stepRun{}
+	if !b.config.DiskImage {
+		steprun.BootDrive = "once=d"
+		steprun.Message = "Starting VM, booting from CD-ROM"
+	} else {
+		steprun.BootDrive = "c"
+		steprun.Message = "Starting VM, booting disk image"
+	}
+
 	steps := []multistep.Step{
 		&common.StepDownload{
 			Checksum:     b.config.ISOChecksum,
@@ -436,10 +445,7 @@ func (b *Builder) Run(ui packer.Ui, hook packer.Hook, cache packer.Cache) (packe
 		new(stepHTTPServer),
 		new(stepForwardSSH),
 		new(stepConfigureVNC),
-		&stepRun{
-			BootDrive: "once=d",
-			Message:   "Starting VM, booting from CD-ROM",
-		},
+		steprun,
 		&stepBootWait{},
 		&stepTypeBootCommand{},
 		&common.StepConnectSSH{

builder/qemu/step_run.go

@@ -82,7 +82,9 @@ func getCommandArgs(bootDrive string, state multistep.StateBag) ([]string, error
 	defaultArgs["-netdev"] = fmt.Sprintf("user,id=user.0,hostfwd=tcp::%v-:22", sshHostPort)
 	defaultArgs["-device"] = fmt.Sprintf("%s,netdev=user.0", config.NetDevice)
 	defaultArgs["-drive"] = fmt.Sprintf("file=%s,if=%s,cache=%s", imgPath, config.DiskInterface, config.DiskCache)
-	defaultArgs["-cdrom"] = isoPath
+	if !config.DiskImage {
+		defaultArgs["-cdrom"] = isoPath
+	}
 	defaultArgs["-boot"] = bootDrive
 	defaultArgs["-m"] = "512M"
 	defaultArgs["-vnc"] = vnc