Update StepCreateInstance to accommodate both ISO and XVA builders

builder/xenserver/common/step_create_instance.go

@@ -12,6 +12,10 @@ import (
 )
 
 type StepCreateInstance struct {
+	// The XVA builder assumes it will boot an instance with an OS installed on its disks
+	// while the ISO builder needs packer to create a disk for an OS to be installed on.
+	AssumePreInstalledOS bool
+
 	instance *xsclient.VMRef
 	vdi      *xsclient.VDIRef
 }
@@ -100,6 +104,7 @@ func (self *StepCreateInstance) Run(ctx context.Context, state multistep.StateBa
 		}
 	}
 
+	if !self.AssumePreInstalledOS {
 		err = c.GetClient().VM.RemoveFromOtherConfig(c.GetSessionRef(), instance, "disks")
 		if err != nil {
 			ui.Error(fmt.Sprintf("Error removing disks from VM other-config: %s", err.Error()))
@@ -138,6 +143,7 @@ func (self *StepCreateInstance) Run(ctx context.Context, state multistep.StateBa
 			ui.Error(fmt.Sprintf("Unable to connect packer disk VDI: %s", err.Error()))
 			return multistep.ActionHalt
 		}
+	}
 
 	// Connect Network
 

builder/xenserver/iso/builder.go

@@ -235,7 +235,9 @@ func (self *Builder) Run(ctx context.Context, ui packer.Ui, hook packer.Hook) (p
 			VdiName:    self.config.ISOName,
 			VdiUuidKey: "isoname_vdi_uuid",
 		},
-		new(xscommon.StepCreateInstance),
+		&xscommon.StepCreateInstance{
+			AssumePreInstalledOS: false,
+		},
 		&xscommon.StepAttachVdi{
 			VdiUuidKey: "floppy_vdi_uuid",
 			VdiType:    xsclient.VbdTypeFloppy,