message: [x] add `--lib` option to disable doctests for `xtest`
  Doc tests add significant overhead when quickly iterating on tests, so
  it's often convenient to disable them.
  Closes:
  Approved by: bmwill
diff: @@ -21,9 +21,12 @@ pub struct Args {
  /// Run test on the provided packages
  package: Vec<String>,
  #[structopt(long, short)]
  - /// Only run unit tests
  + /// Skip running expensive libra testsuite integration tests
  unit: bool,
  #[structopt(long)]
  + /// Test only this package's library unit tests, skipping doctests
  + lib: bool,
  + #[structopt(long)]
  /// Do not fast fail the run if tests (or test executables) fail
  no_fail_fast: bool,
  #[structopt(long)]
  @@ -70,6 +73,9 @@ pub fn run(mut args: Args, xctx: XContext) -> Result<()> {
  if args.no_fail_fast {
  direct_args.push(OsString::from("--no-fail-fast"));
  };
  + if args.lib {
  + direct_args.push(OsString::from("--lib"));
  + }
  let cmd = CargoCommand::Test {
  direct_args: direct_args.as_slice(),
  