common: use cdroms len instead of ISOPaths len

There's special case when option `remove_cdrom` is set that there
would be zero cdrom devices by the time reattach_cdroms processing is
executed, so the comparison to ISOPaths len is wrong. Instead use the
amount of cdroms we have at that point.

Fixes: hashicorp#393

builder/vsphere/common/step_reattach_cdrom.go

@@ -51,7 +51,12 @@ func (s *StepReattachCDRom) Run(_ context.Context, state multistep.StateBag) mul
 
 	// Add the CD-ROM devices to the image based on the value of `reattach_cdroms`.
 	// A valid ISO path is required for this step. The media will subsequently be ejected.
-	nAttachableCdroms := ReattachCDRom - len(s.CDRomConfig.ISOPaths)
+	cdroms, err := vm.CdromDevices()
+	if err != nil {
+		state.Put("error listing cdrom devices: %v", err)
+		return multistep.ActionHalt
+	}
+	nAttachableCdroms := ReattachCDRom - len(cdroms)
 	if nAttachableCdroms < 0 {
 		err = vm.RemoveNCdroms(int(math.Abs(float64(nAttachableCdroms))))
 		if err != nil {

builder/vsphere/common/step_reattach_cdrom_test.go

@@ -41,18 +41,16 @@ func TestStepReattachCDRom_Run(t *testing.T) {
 			expectedAction: multistep.ActionContinue,
 			vmMock: &driver.VirtualMachineMock{
 				ReattachCDRomsCalled: true,
+				CdromDevicesList:     object.VirtualDeviceList{nil},
 			},
 			expectedVmMock: &driver.VirtualMachineMock{
 				EjectCdromsCalled:        true,
-				CdromDevicesList:         object.VirtualDeviceList{nil, nil, nil, nil, nil, nil},
+				CdromDevicesCalled:       true,
+				CdromDevicesList:         object.VirtualDeviceList{nil, nil, nil, nil},
 				ReattachCDRomsCalled:     true,
 				FindSATAControllerCalled: true,
-				AddCdromCalledTimes:      6,
-				AddCdromTypes: []string{
-					"sata", "sata",
-					"sata", "sata",
-					"sata", "sata",
-				},
+				AddCdromCalledTimes:      3,
+				AddCdromTypes: []string{"sata", "sata", "sata"},
 			},
 			fail: false,
 		},
@@ -79,6 +77,7 @@ func TestStepReattachCDRom_Run(t *testing.T) {
 			expectedVmMock: &driver.VirtualMachineMock{
 				RemoveNCdromsCalled:  true,
 				EjectCdromsCalled:    true,
+				CdromDevicesCalled:   true,
 				ReattachCDRomsCalled: true,
 				AddCdromCalledTimes:  0,
 			},
@@ -104,6 +103,7 @@ func TestStepReattachCDRom_Run(t *testing.T) {
 			},
 			expectedVmMock: &driver.VirtualMachineMock{
 				EjectCdromsCalled:    true,
+				CdromDevicesCalled:   true,
 				ReattachCDRomsCalled: true,
 				AddCdromCalledTimes:  0,
 			},