Add support for JOINs without aliases

[jordanw-bq]

Using Docker image amazon/opendistro-for-elasticsearch:1.1.0
Dataset: Flights & Ecommerce sample data (loaded through Kibana)
SQL Plugin version: 1.1.0.1

Example Query:
SELECT AvgTicketPrice AS AvgTicketPrice, Cancelled AS Cancelled, Carrier AS Carrier, DestAirportID AS DestAirportID, DestCityName AS DestCityName, DestCountry AS DestCountry, DestLocation AS DestLocation FROM kibana_sample_data_ecommerce LEFT JOIN kibana_sample_data_flights ON (kibana_sample_data_ecommerce.day_of_week_i = dayOfWeek) LIMIT 50

Results:
No data

{
  "schema": [],
  "total": 10000,
  "datarows": [
    [],
    [],
    [],
    [],
...
    []
  ],
  "size": 50,
  "status": 200
}

Notes:
This is a known limitation of JOINs with Elasticsearch, but Tableau by default will be generating JOINs without aliases.

Expectation:
Support for JOINs without alias

[dai-chen]

Currently alias is required for JOIN.