create a filtered query if there are filters set

Change _normalizeQuery to create a filtered query if the queryObj has filters.  For example:
 
  "query": {
    "filtered": {
      "filter": {
        "and": [
          {
            "term": {
              "tag": "Seasonal"
            }
          }
        ]
      },
      "query": {
        "query_string": {
          "query": "food"
        }
      }
    }
  }