libcontainer/specconv/spec_linux: Add support for (no)iversion

Part of catching runC up with the spec, which punts valid options to
mount(8) [1,2].

[1]: https://github.com/opencontainers/runtime-spec/blame/v1.0.0-rc5/config.md#L68
[2]: opencontainers/runtime-spec#771

Signed-off-by: W. Trevor King <wking@tremily.us>

libcontainer/specconv/spec_linux.go

@@ -647,13 +647,15 @@ func parseMountOptions(options []string) (int, []int, string, int) {
 		"diratime":      {true, unix.MS_NODIRATIME},
 		"dirsync":       {false, unix.MS_DIRSYNC},
 		"exec":          {true, unix.MS_NOEXEC},
+		"iversion":      {false, unix.MS_I_VERSION},
 		"lazytime":      {false, unix.MS_LAZYTIME},
 		"loud":          {true, unix.MS_SILENT},
 		"mand":          {false, unix.MS_MANDLOCK},
 		"noatime":       {false, unix.MS_NOATIME},
 		"nodev":         {false, unix.MS_NODEV},
 		"nodiratime":    {false, unix.MS_NODIRATIME},
 		"noexec":        {false, unix.MS_NOEXEC},
+		"noiversion":    {true, unix.MS_I_VERSION},
 		"nolazytime":    {true, unix.MS_LAZYTIME},
 		"nomand":        {true, unix.MS_MANDLOCK},
 		"norelatime":    {true, unix.MS_RELATIME},