Excluded async_client_sync_server_* tests for poll-cv engine since it
sometimes get stuck (or extremely slow).

(https://github.com/grpc/grpc/issues/8545) created to debug poll-cv
issues with async_client_sync_server perf tests
diff --git a/tools/run_tests/run_tests.py b/tools/run_tests/run_tests.py
index 5aae343..a46783e 100755
--- a/tools/run_tests/run_tests.py
+++ b/tools/run_tests/run_tests.py
@@ -234,6 +234,8 @@
         timeout_scaling = 1
         if polling_strategy == 'poll-cv':
           timeout_scaling *= 5
+        if polling_strategy in target.get('excluded_poll_engines', []):
+          continue;
         if self.config.build_config in target['exclude_configs']:
           continue
         if self.args.iomgr_platform in target.get('exclude_iomgrs', []):