change entity id type as per review comments

Author: srbhaakamai

test/fixtures/monitor_alert-definitions.json

@@ -8,7 +8,7 @@
       "type": "user",
       "description": "A test alert for dbaas service",
       "conditions": [],
-      "entity_ids": [13217],
+      "entity_ids": ["13217"],
       "alert_channels": [],
       "has_more_resources": false,
       "rule_criteria": null,