Add retry for urlopen

Many a times open url returns errors including 503,
handling it by introducing retries.

Signed-off-by: Srikanth Aithal <srikanth.aithal@amd.com>

avocado/utils/download.py

@@ -44,11 +44,18 @@ def url_open(url, data=None, timeout=5):
     :return: file-like object.
     :raises: `URLError`.
     """
-    try:
-        result = urlopen(url, data=data, timeout=timeout)
-    except (socket.timeout, HTTPError) as ex:
-        msg = f"Failed downloading file: {str(ex)}"
-        log.error(msg)
+    retry_attempt = 0
+    while retry_attempt < 10:
+        try:
+            result = urlopen(url, data=data, timeout=timeout)
+            break
+        except (socket.timeout, HTTPError) as ex:
+            msg = f"Failed downloading file: {str(ex)}"
+            log.error(msg)
+            retry_attempt += 1
+            msg = f"retry attempt: {retry_attempt}"
+            log.debug(msg)
+    if "result" not in locals():
         return None
 
     msg = (