test: xrange is not python3

kedifa/test.py

@@ -67,7 +67,7 @@ def retry(callback, try_count=10, try_delay=0.1):
     a true value.
     Always returns the value returned by latest callback invocation.
     """
-    for _ in xrange(try_count):
+    for _ in range(try_count):
       result = callback()
       if result:
         break