Repository: flutter
Issue: Do not run CI test_smoke_test when shard name is invalid, fail faster
Labels: a: tests,team,framework,P2,team-framework,triaged-framework

Sometimes (often) I mess up the shard name when I'm running CI tests locally, but it doesn't tell me the shard name is invalid until after ~45 seconds of smoketests.  Check the shard name and error out _before_ running the smoketests.

```
$ SHARD=add2app_test dart bots/test.dart 
▌11:01:02▐ STARTING ANALYSIS
════════════════════════════════════════════════════════════════════════════════
Running smoketests...
▌11:01:02▐ RUNNING: cd automated_tests; ../../bin/flutter test test_smoke_test/pass_test.dart
▌11:01:12▐ ELAPSED TIME: 9.308s for ../../bin/flutter test test_smoke_test/pass_test.dart in automated_tests
▌11:01:12▐ RUNNING: cd automated_tests; ../../bin/flutter test test_smoke_test/fail_test.dart
▌11:01:15▐ ELAPSED TIME: 3.281s for ../../bin/flutter test test_smoke_test/fail_test.dart in automated_tests
▌11:01:15▐ RUNNING: cd automated_tests; ../../bin/flutter test test_smoke_test/timeout_pass_test.dart
▌11:01:20▐ ELAPSED TIME: 5.515s for ../../bin/flutter test test_smoke_test/timeout_pass_test.dart in automated_tests
▌11:01:20▐ RUNNING: cd automated_tests; ../../bin/flutter test test_smoke_test/timeout_fail_test.dart
▌11:01:27▐ ELAPSED TIME: 6.346s for ../../bin/flutter test test_smoke_test/timeout_fail_test.dart in automated_tests
▌11:01:27▐ RUNNING: cd automated_tests; ../../bin/flutter test test_smoke_test/pending_timer_fail_test.dart
▌11:01:30▐ ELAPSED TIME: 3.442s for ../../bin/flutter test test_smoke_test/pending_timer_fail_test.dart in automated_tests
▌11:01:30▐ RUNNING: cd automated_tests; ../../bin/flutter test test_smoke_test/crash1_test.dart
▌11:01:30▐ RUNNING: cd automated_tests; ../../bin/flutter test test_smoke_test/crash2_test.dart
▌11:01:30▐ RUNNING: cd automated_tests; ../../bin/flutter test test_smoke_test/syntax_error_test.broken_dart
▌11:01:30▐ RUNNING: cd automated_tests; ../../bin/flutter test test_smoke_test/missing_import_test.broken_dart
▌11:01:30▐ RUNNING: cd automated_tests; ../../bin/flutter test test_smoke_test/disallow_error_reporter_modification_test.dart
▌11:01:30▐ RUNNING: cd ../packages/flutter_driver; ../../bin/flutter drive --use-existing-app -t test_driver/failure.dart
▌11:01:34▐ ELAPSED TIME: 3.903s for ../../bin/flutter test test_smoke_test/crash1_test.dart in automated_tests
▌11:01:34▐ ELAPSED TIME: 4.005s for ../../bin/flutter test test_smoke_test/syntax_error_test.broken_dart in automated_tests
▌11:01:36▐ ELAPSED TIME: 5.811s for ../../bin/flutter test test_smoke_test/disallow_error_reporter_modification_test.dart in automated_tests
▌11:01:39▐ ELAPSED TIME: 8.577s for ../../bin/flutter drive --use-existing-app -t test_driver/failure.dart in ../packages/flutter_driver
▌11:01:41▐ ELAPSED TIME: 11.043s for ../../bin/flutter test test_smoke_test/missing_import_test.broken_dart in automated_tests
▌11:01:42▐ ELAPSED TIME: 12.127s for ../../bin/flutter test test_smoke_test/crash2_test.dart in automated_tests
════════════════════════════════════════════════════════════════════════════════
Invalid shard: add2app_test
The available shards are: add_to_app_tests, add_to_app_life_cycle_tests, build_tests, framework_coverage, framework_tests, hostonly_devicelab_tests, tool_coverage, tool_tests, web_tests, web_integration_tests
```