disable nccl2 test on CPU

only mode

python/paddle/fluid/tests/unittests/test_dist_transpiler.py

@@ -661,6 +661,7 @@ class TestLoadSliceVar(TranspilerTest):
 
 class TestNCCL2Transpile(TranspilerTest):
     def test_nccl2_transpile(self):
+        if fluid.core.is_compiled_with_cuda():  #test nccl2 only with cuda
             main = fluid.Program()
             startup = fluid.Program()
             with fluid.program_guard(main, startup):
@@ -677,6 +678,8 @@ class TestNCCL2Transpile(TranspilerTest):
             print([op.type for op in startup.global_block().ops])
             self.assertEqual(startup.global_block().ops[-1].type, "gen_nccl_id")
             self.assertIsNotNone(startup.global_block().vars.get("NCCLID"))
+        else:
+            pass
 
 
 if __name__ == "__main__":