Add --storage-opt graph driver option and pass through to driver

This lets you add storage specific options for the daemon.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)

daemon/graphdriver/aufs/aufs.go

@@ -57,7 +57,7 @@ type Driver struct {
 
 // New returns a new AUFS driver.
 // An error is returned if AUFS is not supported.
-func Init(root string) (graphdriver.Driver, error) {
+func Init(root string, options []string) (graphdriver.Driver, error) {
 	// Try to load the aufs kernel module
 	if err := supportsAufs(); err != nil {
 		return nil, graphdriver.ErrNotSupported

daemon/graphdriver/aufs/aufs_test.go

@@ -17,7 +17,7 @@ var (
 )
 
 func testInit(dir string, t *testing.T) graphdriver.Driver {
-	d, err := Init(dir)
+	d, err := Init(dir, nil)
 	if err != nil {
 		if err == graphdriver.ErrNotSupported {
 			t.Skip(err)