Set all attributes to default values on status URL fetch

We were missing two duration-related attributes here, causing some 500
errors to happen if we had cached status_data around that didn't agree
with our current list of checked mirrors. Don't blow up on the JSON data
fetch by ensuring we provide a value, even if it is out of date.

Signed-off-by: Dan McGee <dan@archlinux.org>

mirrors/utils.py

@@ -88,6 +88,8 @@ def annotate_url(url, url_data):
         ('success_count', 0),
         ('check_count', 0),
         ('completion_pct', None),
+        ('duration_avg', None),
+        ('duration_stddev', None),
         ('last_check', None),
         ('last_sync', None),
         ('delay', None),