Fix ci bug for deleting data files when other test is running (#21661)

* fix ci bug for deleting data files, test=develop

* update, test=develop

python/paddle/fluid/contrib/slim/tests/test_post_training_quantization_mobilenetv1.py

@@ -133,9 +133,10 @@ class TestPostTrainingQuantization(unittest.TestCase):
                                                         "small_data", False)
 
         # reader/decorator.py requires the relative path to the data folder
-        cmd = 'rm -rf {0} && ln -s {1} {0}'.format("data",
-                                                   self.data_cache_folder)
-        os.system(cmd)
+        if not os.path.exists("./data/ILSVRC2012"):
+            cmd = 'rm -rf {0} && ln -s {1} {0}'.format("data",
+                                                       self.data_cache_folder)
+            os.system(cmd)
 
         self.batch_size = 1 if os.environ.get('DATASET') == 'full' else 50
         self.sample_iterations = 50 if os.environ.get(