allow flaky ros2_cpp_tests (mvukov#342)

ros2/ament.bzl

@@ -329,7 +329,7 @@ def py_launcher(name, deps, idl_deps = None, **kwargs):
 
 def split_kwargs(**kwargs):
     """Split kwargs into those to be forwarded to the actual binary target and launcher target respectively."""
-    launcher_attrs = ["args", "env", "size", "tags", "timeout", "visibility"]
+    launcher_attrs = ["args", "env", "flaky", "size", "tags", "timeout", "visibility"]
     launcher_target_kwargs = {attr: kwargs.pop(attr) for attr in launcher_attrs if attr in kwargs}
     return launcher_target_kwargs, kwargs