caucase.http: Do not risk modifying dictionary during iteration.

caucase/http.py

@@ -1062,7 +1062,7 @@ def manage(argv=None, stdout=sys.stdout):
       db_path,
       table_prefix='cas',
     )
-    for identifier, ca_pair in import_ca_dict.items():
+    for identifier, ca_pair in list(import_ca_dict.items()):
       found_from = ', '.join(ca_pair['from'])
       crt = ca_pair['crt']
       if crt is None: