libcontainer/specconv/spec_linux: Add support for silent and loud

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

@@ -648,6 +648,7 @@ func parseMountOptions(options []string) (int, []int, string, int) {
 		"dirsync":       {false, unix.MS_DIRSYNC},
 		"exec":          {true, unix.MS_NOEXEC},
 		"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},
@@ -663,6 +664,7 @@ func parseMountOptions(options []string) (int, []int, string, int) {
 		"remount":       {false, unix.MS_REMOUNT},
 		"ro":            {false, unix.MS_RDONLY},
 		"rw":            {true, unix.MS_RDONLY},
+		"silent":        {false, unix.MS_SILENT},
 		"strictatime":   {false, unix.MS_STRICTATIME},
 		"suid":          {true, unix.MS_NOSUID},
 		"sync":          {false, unix.MS_SYNCHRONOUS},