Update octodns/provider/plan.py

Refactor zone vs provider choice to read more cleanly

Co-authored-by: Ross McFarland <rwmcfa1@gmail.com>

octodns/provider/plan.py

@@ -57,15 +57,16 @@ class Plan(object):
         # them and/or is as safe as possible.
         self.changes = sorted(changes)
         self.exists = exists
-        self.update_pcent_threshold = update_pcent_threshold
-        self.delete_pcent_threshold = delete_pcent_threshold
 
         # Zone thresholds take precedence over provider
         if existing and existing.update_pcent_threshold is not None:
             self.update_pcent_threshold = existing.update_pcent_threshold
+        else:
+            self.update_pcent_threshold = update_pcent_threshold
         if existing and existing.delete_pcent_threshold is not None:
             self.delete_pcent_threshold = existing.delete_pcent_threshold
-
+        else:
+            self.delete_pcent_threshold = delete_pcent_threshold
         change_counts = {'Create': 0, 'Delete': 0, 'Update': 0}
         for change in changes:
             change_counts[change.__class__.__name__] += 1