[UnitTest]Enhance grep syntax to avoid random failed of test_dist_mnist_dgc_nccl (#32946)

* Enhance grep syntax to avoid random failed

* Enhance grep syntax to avoid random failed

Author: Aurelius84

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

@@ -25,12 +25,15 @@
 
 
 def count_of_sparse_all_reduce_calls(file_name):
-    cmd = 'grep sparse_all_reduce_op_handle ' + file_name + ' | grep in_numel | wc -l'
+    # NOTE(Aurelius84): The log file contains some binary contents that causes error
+    # while `grep`. So we add `-a` to fix it.
+    # -a, --text equivalent to --binary-files=text, make binaries equivalent to text.
+    cmd = 'grep -a sparse_all_reduce_op_handle ' + file_name + ' | grep in_numel | wc -l'
     child = subprocess.Popen(cmd, stdout=subprocess.PIPE, shell=True)
     result = child.communicate()[0]
     print('test_info: result = ' + str(result))
 
-    # note. in python3, result is b'num', != 'num' 
+    # NOTE: in python3, result is b'num', != 'num'
     return int(result)
 
 
@@ -59,7 +62,7 @@ def tearDown(self):
             # only 1 layer use dgc now, run_step=5, rampup_begin_step=2, so 1 * (5 - 2) = 3
 
             # temp close this test. In python3 CI, the log is right, but the result
-            # has a problem, may be in multi process mode, log is not writed in time.  
+            # has a problem, may be in multi process mode, log is not written in time.
             # self.assertEqual(result, 3)