Catch exception in download (#28090)

* cat exeception in request download; test=develop

* add re-try in download; test=develop

python/paddle/dataset/common.py

@@ -88,6 +88,7 @@ def download(url, module_name, md5sum, save_name=None):
         sys.stderr.write("Cache file %s not found, downloading %s \n" %
                          (filename, url))
         sys.stderr.write("Begin to download\n")
+        try:
             r = requests.get(url, stream=True)
             total_length = r.headers.get('content-length')
 
@@ -109,6 +110,9 @@ def download(url, module_name, md5sum, save_name=None):
                         if log_index % log_interval == 0:
                             sys.stderr.write(".")
                         sys.stdout.flush()
+        except Exception as e:
+            # re-try
+            continue
     sys.stderr.write("\nDownload finished\n")
     sys.stdout.flush()
     return filename