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/vfs/driver.go

@@ -12,7 +12,7 @@ func init() {
 	graphdriver.Register("vfs", Init)
 }
 
-func Init(home string) (graphdriver.Driver, error) {
+func Init(home string, options []string) (graphdriver.Driver, error) {
 	d := &Driver{
 		home: home,
 	}