[impala] Support query timeout

QUERY_TIMEOUT_S

If a client sets QUERY_TIMEOUT_S > 0, the query will be timed out (i.e. cancelled) if Impala does not do any work for that query within QUERY_TIMEOUT_S seconds, i.e. it doesn't spend time producing results nor sending them to the client.

If Impala has --idle_query_timeout=X set on the server side, that value X is the maximum query timeout that the user can specify, and if none is specified, X is the default.

Query timeout is always enabled, so if Hue sets the query option, the query will eventually time out.