#OBS-I77 : query api changes to check datasource availability

[JeraldJF]

Description

https://sprints.zoho.in/workspace/sanketika#P2/itemdetails/I77

Query api enhancements

1. Check for datasource in the druid. If not present then throw error {"status":404, "message":"Datasource is not available for quering"}
2. If datasource in available in the druid but if segments are not fully loaded then throw error {"status":416, "message":"Datasource not fully available for quering"}