message: datatest: enable listing of tests
  Teach test binaries built using `datatest-stable` to be able to list the
  names of each test with the `--list` option. This matches the behavior
  of the `--list` option with test binaries built using the default test
  harness.
  Closes:
  Approved by: sausagee
diff: @@ -32,12 +32,25 @@ struct TestOpts {
  #[structopt(long)]
  /// We already can't capture anything but we don't want arg parsing to fail so this is a noop
  nocapture: bool,
  + #[structopt(long)]
  + /// List all tests
  + list: bool,
  }
  pub fn runner(reqs: &[Requirements]) {
  let options = TestOpts::from_args();
  - let tests = reqs.iter().flat_map(|req| req.expand()).collect();
  + let tests: Vec<Test> = reqs.iter().flat_map(|req| req.expand()).collect();
  +
  + if options.list {
  + for test in &tests {
  + println!("{}: test", test.name);
  + }
  +
  + println!();
  + println!("{} tests, 0 benchmarks", tests.len());
  + return;
  + }
  match run_tests(options, tests) {
  Ok(true) => {}
  