Check for specific watch in watch test

Original commit: elastic/x-pack-elasticsearch@e778f14714

plugin/src/test/resources/rest-api-spec/test/watcher/ack_watch/10_basic.yaml

@@ -48,6 +48,7 @@
   - do:
       search:
         index: .watches
+        body: { "query": { "term": { "_id": "my_watch" } } }
   - match: { hits.total: 1 }
   - match: { hits.hits.0._source._status.actions.test_index.ack.state: "awaits_successful_execution" }