[test] Wait for EE to quiesce in RLSEnd2endTest teardown (#36553)

Closes #36553

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/36553 from drfloob:cleaner-RlsEnd2endTest-shutdown f16b5aac3e
PiperOrigin-RevId: 631496415

CMakeLists.txt

@@ -26337,6 +26337,7 @@ add_executable(rls_end2end_test
   ${_gRPC_PROTO_GENS_DIR}/src/proto/grpc/testing/xds/v3/orca_load_report.grpc.pb.cc
   ${_gRPC_PROTO_GENS_DIR}/src/proto/grpc/testing/xds/v3/orca_load_report.pb.h
   ${_gRPC_PROTO_GENS_DIR}/src/proto/grpc/testing/xds/v3/orca_load_report.grpc.pb.h
+  test/core/event_engine/event_engine_test_utils.cc
   test/core/test_util/fake_stats_plugin.cc
   test/core/test_util/test_lb_policies.cc
   test/cpp/end2end/rls_end2end_test.cc

build_autogenerated.yaml

@@ -17596,6 +17596,7 @@ targets:
   run: false
   language: c++
   headers:
+  - test/core/event_engine/event_engine_test_utils.h
   - test/core/test_util/fake_stats_plugin.h
   - test/core/test_util/test_lb_policies.h
   - test/cpp/end2end/counted_service.h
@@ -17608,6 +17609,7 @@ targets:
   - src/proto/grpc/testing/echo_messages.proto
   - src/proto/grpc/testing/simple_messages.proto
   - src/proto/grpc/testing/xds/v3/orca_load_report.proto
+  - test/core/event_engine/event_engine_test_utils.cc
   - test/core/test_util/fake_stats_plugin.cc
   - test/core/test_util/test_lb_policies.cc
   - test/cpp/end2end/rls_end2end_test.cc

test/cpp/end2end/BUILD

@@ -584,6 +584,7 @@ grpc_cc_test(
         "//src/proto/grpc/testing:echo_messages_proto",
         "//src/proto/grpc/testing:echo_proto",
         "//src/proto/grpc/testing/duplicate:echo_duplicate_proto",
+        "//test/core/event_engine:event_engine_test_utils",
         "//test/core/test_util:fake_stats_plugin",
         "//test/core/test_util:grpc_test_util",
         "//test/core/test_util:test_lb_policies",

test/cpp/end2end/rls_end2end_test.cc

@@ -58,6 +58,7 @@
 #include "src/proto/grpc/lookup/v1/rls.grpc.pb.h"
 #include "src/proto/grpc/lookup/v1/rls.pb.h"
 #include "src/proto/grpc/testing/echo.grpc.pb.h"
+#include "test/core/event_engine/event_engine_test_utils.h"
 #include "test/core/test_util/fake_stats_plugin.h"
 #include "test/core/test_util/port.h"
 #include "test/core/test_util/resolve_localhost_ip46.h"
@@ -175,6 +176,8 @@ class RlsEnd2endTest : public ::testing::Test {
 
   static void TearDownTestSuite() {
     grpc_shutdown_blocking();
+    WaitForSingleOwner(
+        grpc_event_engine::experimental::GetDefaultEventEngine());
     grpc_core::CoreConfiguration::Reset();
   }