add wait on delay (#794)

elasticsearch/transport.py

@@ -294,7 +294,7 @@ class Transport(object):
 
         if body is not None:
             try:
-                body = body.encode('utf-8', 'surrogatepass')            
+                body = body.encode('utf-8', 'surrogatepass')
             except (UnicodeDecodeError, AttributeError):
                 # bytes/str - no need to re-encode
                 pass
@@ -311,6 +311,10 @@ class Transport(object):
             connection = self.get_connection()
 
             try:
+                # add a delay before attempting the next retry
+                # 0, 1, 3, 7, etc...
+                delay = 2**attempt - 1
+                time.sleep(delay)
                 status, headers_response, data = connection.perform_request(method, url, params, body, headers=headers, ignore=ignore, timeout=timeout)
 
             except TransportError as e: