Merge pull request #660 from jason-simmons/apk_output_label

Add output to "flutter apk" indicating where the APK file was written

packages/flutter_tools/lib/src/commands/apk.dart

@@ -211,6 +211,8 @@ class ApkCommand extends FlutterCommand {
       ensureDirectoryExists(finalApk.path);
       builder.align(unalignedApk, finalApk);
 
+      print('APK generated: ${finalApk.path}');
+
       return 0;
     } finally {
       tempDir.deleteSync(recursive: true);