1434-Added homebrew cask support for VMware Fusion

This aims to lookup for Vmware Fusion required binaries (vmrun and vmware-vdiskmanager) in the system path first before falling back in the default Vmware Fusion installing path.
Thereby, the vmwarefusion docker-machine driver can now be used even if Vmware Fusion is not installed in its default location (with brew cask for example).
Signed-off-by: Jean-Christophe Lagache <jclagache@gmail.com>

drivers/vmwarefusion/vmrun_darwin.go

@@ -8,16 +8,16 @@ import (
 	"bytes"
 	"errors"
 	"fmt"
+	"github.com/docker/machine/log"
 	"os"
 	"os/exec"
+	"path/filepath"
 	"strings"
-
-	"github.com/docker/machine/log"
 )
 
 var (
-	vmrunbin    = "/Applications/VMware Fusion.app/Contents/Library/vmrun"
-	vdiskmanbin = "/Applications/VMware Fusion.app/Contents/Library/vmware-vdiskmanager"
+	vmrunbin    = setVmwareCmd("vmrun")
+	vdiskmanbin = setVmwareCmd("vmware-vdiskmanager")
 )
 
 var (
@@ -26,6 +26,14 @@ var (
 	ErrVMRUNNotFound   = errors.New("VMRUN not found")
 )
 
+// detect the vmrun and vmware-vdiskmanager cmds' path if needed
+func setVmwareCmd(cmd string) string {
+	if path, err := exec.LookPath(cmd); err == nil {
+		return path
+	}
+	return filepath.Join("/Applications/VMware Fusion.app/Contents/Library/", cmd)
+}
+
 func vmrun(args ...string) (string, string, error) {
 	cmd := exec.Command(vmrunbin, args...)
 	if os.Getenv("DEBUG") != "" {