pkg/mount: Add "private" flag

This allows "mount --make-private" functionallity.

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

pkg/mount/flags_linux.go

@@ -38,6 +38,7 @@ func parseOptions(options string) (int, string) {
 		"nodiratime":    {false, syscall.MS_NODIRATIME},
 		"bind":          {false, syscall.MS_BIND},
 		"rbind":         {false, syscall.MS_BIND | syscall.MS_REC},
+		"private":       {false, syscall.MS_PRIVATE},
 		"relatime":      {false, syscall.MS_RELATIME},
 		"norelatime":    {true, syscall.MS_RELATIME},
 		"strictatime":   {false, syscall.MS_STRICTATIME},