Reduce xDS GCE interop framework to only run ping_pong (#27355)

* Reduce xDS GCE interop framework to only run ping_pong

* Revert changes in PHP and Ruby

tools/internal_ci/linux/grpc_xds_bazel_python_test_in_docker.sh

@@ -68,7 +68,7 @@ export PYTHONUNBUFFERED=true
 GRPC_VERBOSITY=debug GRPC_TRACE=xds_client,xds_resolver,xds_cluster_manager_lb,cds_lb,xds_cluster_resolver_lb,priority_lb,xds_cluster_impl_lb,weighted_target_lb "$PYTHON" \
   tools/run_tests/run_xds_tests.py \
     --halt_after_fail \
-    --test_case="all,circuit_breaking,timeout,fault_injection" \
+    --test_case="ping_pong" \
     --project_id=grpc-testing \
     --project_num=830293263384 \
     --source_image=projects/grpc-testing/global/images/xds-test-server-4 \

tools/internal_ci/linux/grpc_xds_bazel_test_in_docker.sh

@@ -70,7 +70,7 @@ bazel build test/cpp/interop:xds_interop_client
 GRPC_VERBOSITY=debug GRPC_TRACE=xds_client,xds_resolver,xds_cluster_manager_lb,cds_lb,xds_cluster_resolver_lb,priority_lb,xds_cluster_impl_lb,weighted_target_lb "$PYTHON" \
   tools/run_tests/run_xds_tests.py \
     --halt_after_fail \
-    --test_case="all,circuit_breaking,timeout,fault_injection,csds" \
+    --test_case="ping_pong" \
     --project_id=grpc-testing \
     --project_num=830293263384 \
     --source_image=projects/grpc-testing/global/images/xds-test-server-4 \

tools/internal_ci/linux/grpc_xds_csharp_test_in_docker.sh

@@ -68,7 +68,7 @@ python tools/run_tests/run_tests.py -l csharp -c opt --build_only
 GRPC_VERBOSITY=debug GRPC_TRACE=xds_client,xds_resolver,xds_cluster_manager_lb,cds_lb,xds_cluster_resolver_lb,priority_lb,xds_cluster_impl_lb,weighted_target_lb "$PYTHON" \
   tools/run_tests/run_xds_tests.py \
     --halt_after_fail \
-    --test_case="all,path_matching,header_matching" \
+    --test_case="ping_pong" \
     --project_id=grpc-testing \
     --project_num=830293263384 \
     --source_image=projects/grpc-testing/global/images/xds-test-server-2 \