Fix normalize_user_scripts in `coriolis.api.v1.utils` module

coriolis/api/v1/utils.py

@@ -122,13 +122,13 @@ def normalize_user_scripts(user_scripts, instances):
         selected instances for the replica/migration """
     if user_scripts is None:
         user_scripts = {}
-    for instance in user_scripts.get('instances', {}).keys():
+    for instance in list(user_scripts.get('instances', {}).keys()):
         if instance not in instances:
             LOG.warn("Removing provided instance '%s' from user_scripts body "
                      "because it's not included in one of the selected "
                      "instances for this replica/migration: %s",
                      instance, instances)
-            user_scripts.pop(instance, None)
+            user_scripts['instances'].pop(instance, None)
 
     return user_scripts