message: [management] add config to validator-config command
  Closes:
  Approved by: gregnazario
diff: @@ -198,15 +198,19 @@ fn decode_address(raw_address: RawNetworkAddress) -> Result<NetworkAddress, Erro
  #[derive(Debug, StructOpt)]
  pub struct ValidatorConfig {
  - #[structopt(long, help = "JSON-RPC Endpoint (e.g. http://localhost:8080")]
  - json_server: String,
  + #[structopt(flatten)]
  + config: libra_management::config::ConfigPath,
  + /// JSON-RPC Endpoint (e.g. http://localhost:8080)
  + #[structopt(long, required_unless = "config")]
  + json_server: Option<String>,
  #[structopt(long, help = "Validator account address to display the config")]
  account_address: AccountAddress,
  }
  impl ValidatorConfig {
  pub fn execute(self) -> Result<libra_types::validator_config::ValidatorConfig, Error> {
  - let client = JsonRpcClientWrapper::new(self.json_server);
  + let config = self.config.load()?.override_json_server(&self.json_server);
  + let client = JsonRpcClientWrapper::new(config.json_server);
  client.validator_config(self.account_address)
  }
  }
  