Support future versions of Parallels by using the latest driver

If the Parallels Desktop for Mac version is higher than the latest
Packer driver use the latest available driver. Before this Packer needed
to be updated with every new version of PD even if there was no change
to the driver.

builder/parallels/common/driver.go

@@ -5,6 +5,7 @@ import (
 	"log"
 	"os/exec"
 	"runtime"
+	"strconv"
 	"strings"
 )
 
@@ -125,6 +126,14 @@ func NewDriver() (Driver, error) {
 		supportedVersions = append(supportedVersions, v)
 	}
 
+	latestDriver := 11
+	version, _ := drivers[strconv.Itoa(latestDriver)].Version()
+	majVer, _ := strconv.Atoi(strings.SplitN(version, ".", 2)[0])
+	if majVer > latestDriver {
+		log.Printf("Your version of Parallels Desktop for Mac is %s, Packer will use driver for version %d.", version, latestDriver)
+		return drivers[strconv.Itoa(latestDriver)], nil
+	}
+
 	return nil, fmt.Errorf(
 		"Unable to initialize any driver. Supported Parallels Desktop versions: "+
 			"%s\n", strings.Join(supportedVersions, ", "))