[REST-TEST] Use catch: missing instead of ignore: 404

Some of the non java clients don't return the body on an ignore: 404 so we must use catch missing instead.

Original commit: elastic/x-pack-elasticsearch@a10582691c

rest-api-spec/test/get_watch/20_missing.yaml

@@ -6,9 +6,8 @@
 
 
   - do:
+      catch: missing
       watcher.get_watch:
         id: "missing_watch"
-        ignore: 404
-
   - match: { found : false}
   - match: { _id: "missing_watch" }