Tests: Added some tests for proper 404 responses on watch actions (elastic/elasticsearch#4620)

Relates elastic/elasticsearch#4616 elastic/elasticsearch#4617

Original commit: elastic/x-pack-elasticsearch@7f73792507

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

@@ -50,3 +50,13 @@
         id: "my_watch"
 
   - match: { found: true }
+
+---
+"Non existent watch returns 404":
+  - do:
+      cluster.health:
+          wait_for_status: yellow
+  - do:
+      xpack.watcher.ack_watch:
+        watch_id: "non-existent-watch"
+      catch: missing

elasticsearch/src/test/resources/rest-api-spec/test/watcher/activate_watch/10_basic.yaml

@@ -75,3 +75,19 @@
         id: "my_watch"
 
   - match: { found: true }
+
+---
+"Non existent watch returns 404":
+  - do:
+      cluster.health:
+          wait_for_status: yellow
+
+  - do:
+      xpack.watcher.activate_watch:
+        watch_id: "non-existent-watch"
+      catch: missing
+
+  - do:
+      xpack.watcher.deactivate_watch:
+        watch_id: "non-existent-watch"
+      catch: missing

elasticsearch/src/test/resources/rest-api-spec/test/watcher/delete_watch/10_basic.yaml

@@ -42,3 +42,14 @@
       xpack.watcher.delete_watch:
         id: "my_watch"
   - match: { found: true }
+
+---
+"Non existent watch returns 404":
+  - do:
+      cluster.health:
+          wait_for_status: yellow
+
+  - do:
+      xpack.watcher.delete_watch:
+        id: "non-existent-watch"
+      catch: missing