Improve test.dart output (#14333)

It adds lines like `SHARD=analyze` to each shard, and a message like `Contents of packages/flutter_localizations/lib/src/l10n/localizations.dart matches output of gen_localizations.dart script.`  to the analysis shard.

dev/bots/test.dart

@@ -49,11 +49,13 @@ Future<Null> main(List<String> args) async {
   if (shard != null) {
     if (!_kShards.containsKey(shard))
       throw new ArgumentError('Invalid shard: $shard');
+    print('${bold}SHARD=$shard$reset');
     await _kShards[shard]();
   } else {
     for (String currentShard in _kShards.keys) {
       print('${bold}SHARD=$currentShard$reset');
       await _kShards[currentShard]();
+      print('');
     }
   }
 }
@@ -91,6 +93,7 @@ Future<Null> _verifyInternationalizations() async {
       ..writeln('Did you forget to run gen_localizations.dart after updating a .arb file?');
     exit(1);
   }
+  print('Contents of $localizationsFile matches output of gen_localizations.dart script.');
 }
 
 Future<Null> _analyzeRepo() async {