daemon/mountVolumes: no need to specify fstype

For bind mounts, fstype argument to mount(2) is ignored.
Usual convention is either empty string or "none".

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

daemon/bindmount_unix.go

@@ -1,5 +0,0 @@
-// +build linux freebsd
-
-package daemon // import "github.com/docker/docker/daemon"
-
-const bindMountType = "bind"

daemon/volumes_unix.go

@@ -142,7 +142,7 @@ func (daemon *Daemon) mountVolumes(container *container.Container) error {
 			writeMode = "rw"
 		}
 		opts := strings.Join([]string{bindMode, writeMode}, ",")
-		if err := mount.Mount(m.Source, dest, bindMountType, opts); err != nil {
+		if err := mount.Mount(m.Source, dest, "", opts); err != nil {
 			return err
 		}