Make transformer unittest serial

Author: velconia

python/paddle/fluid/tests/unittests/CMakeLists.txt

@@ -49,6 +49,7 @@ list(REMOVE_ITEM TEST_OPS test_dist_train)
 list(REMOVE_ITEM TEST_OPS test_parallel_executor_crf)
 list(REMOVE_ITEM TEST_OPS test_parallel_executor_fetch_feed)
 list(REMOVE_ITEM TEST_OPS test_dist_se_resnext)
+list(REMOVE_ITEM TEST_OPS test_dist_transformer)
 foreach(TEST_OP ${TEST_OPS})
     py_test_modules(${TEST_OP} MODULES ${TEST_OP})
 endforeach(TEST_OP)
@@ -62,3 +63,4 @@ endif()
 py_test_modules(test_parallel_executor_crf MODULES test_parallel_executor_crf SERIAL)
 py_test_modules(test_parallel_executor_fetch_feed MODULES test_parallel_executor_fetch_feed SERIAL)
 py_test_modules(test_dist_se_resnext MODULES test_dist_se_resnext SERIAL)
+py_test_modules(test_dist_transformer MODULES test_dist_transformer SERIAL)