message: nydusify: add command line arg fs-version check
  Add fs-version value check, should be either "5" or "6".
diff: @@ -226,6 +226,12 @@ func main() {
  return fmt.Errorf("--backend-type should be one of %v", possibleBackendTypes)
  }
  + fsVersion := c.String("fs-version")
  + possibleFsVersions := []string{"5", "6"}
  + if !isPossibleValue(possibleFsVersions, fsVersion) {
  + return fmt.Errorf("--fs-version should be one of %v", possibleFsVersions)
  + }
  +
  // This only works for OSS backend rightnow
  backendConfig, err := parseBackendConfig(c.String("backend-config"), c.String("backend-config-file"))
  if err != nil {
  @@ -312,7 +318,7 @@ func main() {
  NydusifyVersion: version,
  Source: c.String("source"),
  - FsVersion: c.String("fs-version"),
  + FsVersion: fsVersion,
  ChunkDict: converter.ChunkDictOpt{
  Args: c.String("chunk-dict"),
  