message: [libra_swarm] disable logging by default
  make disable logging default behavior for libra_swarm playground
diff: @@ -15,9 +15,9 @@ struct Args {
  /// Number of nodes to start (1 by default)
  #[structopt(short = "n", long = "num_nodes")]
  pub num_nodes: Option<usize>,
  - /// Disable logging (for performance testing)"
  - #[structopt(short = "d", long = "disable_logging")]
  - pub disable_logging: bool,
  + /// Enable logging
  + #[structopt(short = "l", long = "enable_logging")]
  + pub enable_logging: bool,
  /// Start client
  #[structopt(short = "s", long = "start_client")]
  pub start_client: bool,
  @@ -45,7 +45,7 @@ fn main() {
  let swarm = LibraSwarm::launch_swarm(
  num_nodes,
  - args.disable_logging,
  + !args.enable_logging,
  faucet_account_keypair,
  false, /* tee_logs */
  args.config_dir.clone(),
  