ESXi builds require we store the value of displayName in the statebag

The value of displayName is needed by later steps:
* When determining the IP address of the build VM
* When exporting the VM using ovftool

By default Packer will configure the VMX so `displayName` is equal to
the value defined for `vm_name` in the build template. However, it is
possible (and sometimes desirable) to set a custom value for
`displayName`.
Users can set a custom `displayName` through use of the `vmx_data`
option in their template.

builder/vmware/common/step_configure_vmx.go

@@ -16,6 +16,9 @@ import (
 //
 // Uses:
 //   vmx_path string
+//
+// Produces:
+//   display_name string - Value of the displayName key set in the VMX file
 type StepConfigureVMX struct {
 	CustomData map[string]string
 	SkipFloppy bool
@@ -73,6 +76,19 @@ func (s *StepConfigureVMX) Run(_ context.Context, state multistep.StateBag) mult
 		return multistep.ActionHalt
 	}
 
+	// If the build is taking place on a remote ESX server, the displayName
+	// will be needed for discovery of the VM's IP address and for export
+	// of the VM. The displayName key should always be set in the VMX file,
+	// so error if we don't find it
+	if displayName, ok := vmxData["displayname"]; !ok { // Packer converts key names to lowercase!
+		err := fmt.Errorf("Error: Could not get value of displayName from VMX data")
+		state.Put("error", err)
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	} else {
+		state.Put("display_name", displayName)
+	}
+
 	return multistep.ActionContinue
 }