feat: Make firmware configurable

I extracted the changes as-is from vatesfr#28.

Author: mboutet

builder/xenserver/common/config.go

@@ -33,6 +33,8 @@ type Config struct {
 	InstallTimeout    time.Duration ``
 	SourcePath        string        `mapstructure:"source_path"`
 
+	Firmware string `mapstructure:"firmware"`
+
 	ctx interpolate.Context
 }
 

builder/xenserver/common/config.hcl2spec.go

@@ -16,6 +16,7 @@ func (self *StepStartVmPaused) Run(ctx context.Context, state multistep.StateBag
 
 	c := state.Get("client").(*Connection)
 	ui := state.Get("ui").(packer.Ui)
+	config := state.Get("config").(Config)
 
 	ui.Say("Step: Start VM Paused")
 
@@ -34,7 +35,7 @@ func (self *StepStartVmPaused) Run(ctx context.Context, state multistep.StateBag
 		return multistep.ActionHalt
 	}
 
-	err = c.client.VM.SetHVMBootParams(c.session, instance, map[string]string{"order": "cd"})
+	err = c.client.VM.SetHVMBootParams(c.session, instance, map[string]string{"order": "cd", "firmware": config.Firmware})
 	if err != nil {
 		ui.Error(fmt.Sprintf("Unable to set HVM boot params: %s", err.Error()))
 		return multistep.ActionHalt

builder/xenserver/common/step_start_vm_paused.go

@@ -77,6 +77,10 @@ func (self *Builder) Prepare(raws ...interface{}) (params []string, warns []stri
 		self.config.CloneTemplate = "Other install media"
 	}
 
+	if self.config.Firmware == "" {
+		self.config.Firmware = "bios"
+	}
+
 	if len(self.config.PlatformArgs) == 0 {
 		pargs := make(map[string]string)
 		pargs["viridian"] = "false"