message: add config::incluster_config::load_default_ns()
diff: @@ -9,6 +9,7 @@ pub const SERVICE_HOSTENV: &str = "KUBERNETES_SERVICE_HOST";
  pub const SERVICE_PORTENV: &str = "KUBERNETES_SERVICE_PORT";
  const SERVICE_TOKENFILE: &str = "/var/run/secrets/kubernetes.io/serviceaccount/token";
  const SERVICE_CERTFILE: &str = "/var/run/secrets/kubernetes.io/serviceaccount/ca.crt";
  +const SERVICE_DEFAULT_NS: &str = "/var/run/secrets/kubernetes.io/serviceaccount/namespace";
  /// Returns kubernetes address from specified environment variables.
  pub fn kube_server() -> Option<String> {
  @@ -26,15 +27,20 @@ fn kube_port() -> Option<String> {
  /// Returns token from specified path in cluster.
  pub fn load_token() -> Result<String, Error> {
  - utils::data_or_file(&None, &Some(SERVICE_TOKENFILE.to_string()))
  + utils::data_or_file(&None, &Some(SERVICE_TOKENFILE))
  }
  /// Returns certification from specified path in cluster.
  pub fn load_cert() -> Result<X509, Error> {
  - let ca = utils::data_or_file_with_base64(&None, &Some(SERVICE_CERTFILE.to_string()))?;
  + let ca = utils::data_or_file_with_base64(&None, &Some(SERVICE_CERTFILE))?;
  X509::from_pem(&ca).map_err(Error::from)
  }
  +/// Returns the default namespace from specified path in cluster.
  +pub fn load_default_ns() -> Result<String, Error> {
  + utils::data_or_file(&None, &Some(SERVICE_DEFAULT_NS))
  +}
  +
  #[test]
  fn test_kube_host() {
  let expected = "fake.io";
  