builder/parallels: Add "CompactDisk" driver function

This function compacts the specified virtual disk image.

builder/parallels/common/driver.go

@@ -15,6 +15,9 @@ import (
 // versions out of the builder steps, so sometimes the methods are
 // extremely specific.
 type Driver interface {
+	// Compact a virtual disk image.
+	CompactDisk(string) error
+
 	// Adds new CD/DVD drive to the VM and returns name of this device
 	DeviceAddCdRom(string, string) (string, error)
 

builder/parallels/common/driver_9.go

@@ -98,6 +98,33 @@ func getAppPath(bundleId string) (string, error) {
 	return pathOutput, nil
 }
 
+func (d *Parallels9Driver) CompactDisk(diskPath string) error {
+	prlDiskToolPath, err := exec.LookPath("prl_disk_tool")
+	if err != nil {
+		return err
+	}
+
+	// Analyze the disk content and remove unused blocks
+	command := []string{
+		"compact",
+		"--hdd", diskPath,
+	}
+	if err := exec.Command(prlDiskToolPath, command...).Run(); err != nil {
+		return err
+	}
+
+	// Remove null blocks
+	command = []string{
+		"compact", "--buildmap",
+		"--hdd", diskPath,
+	}
+	if err := exec.Command(prlDiskToolPath, command...).Run(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
 func (d *Parallels9Driver) DeviceAddCdRom(name string, image string) (string, error) {
 	command := []string{
 		"set", name,

builder/parallels/common/driver_mock.go

@@ -5,6 +5,10 @@ import "sync"
 type DriverMock struct {
 	sync.Mutex
 
+	CompactDiskCalled bool
+	CompactDiskPath   string
+	CompactDiskErr    error
+
 	DeviceAddCdRomCalled bool
 	DeviceAddCdRomName   string
 	DeviceAddCdRomImage  string
@@ -59,6 +63,12 @@ type DriverMock struct {
 	IpAddressError  error
 }
 
+func (d *DriverMock) CompactDisk(path string) error {
+	d.CompactDiskCalled = true
+	d.CompactDiskPath = path
+	return d.CompactDiskErr
+}
+
 func (d *DriverMock) DeviceAddCdRom(name string, image string) (string, error) {
 	d.DeviceAddCdRomCalled = true
 	d.DeviceAddCdRomName = name