Fix client_lb_end2end_test flake

src/core/lib/surface/init.cc

@@ -243,7 +243,7 @@ int grpc_is_initialized(void) {
 void grpc_maybe_wait_for_async_shutdown(void) {
   gpr_once_init(&g_basic_init, do_basic_init);
   grpc_core::MutexLock lock(&g_init_mu);
-  while (g_shutting_down) {
+  while (g_shutting_down || g_initializations > 0) {
     gpr_cv_wait(g_shutting_down_cv, &g_init_mu,
                 gpr_inf_future(GPR_CLOCK_REALTIME));
   }

test/cpp/end2end/client_lb_end2end_test.cc

@@ -50,6 +50,7 @@
 #include "src/core/lib/gprpp/ref_counted_ptr.h"
 #include "src/core/lib/iomgr/tcp_client.h"
 #include "src/core/lib/security/credentials/fake/fake_credentials.h"
+#include "src/core/lib/surface/init.h"
 #include "src/cpp/client/secure_credentials.h"
 #include "src/cpp/server/secure_server_credentials.h"
 
@@ -239,6 +240,7 @@ class ClientLbEnd2endTest : public ::testing::Test {
     servers_.clear();
     creds_.reset();
     grpc_shutdown_blocking();
+    grpc_maybe_wait_for_async_shutdown();
   }
 
   void CreateServers(size_t num_servers,