Support subquery inside tick script

InfluxDB 1.2 supports subqueries, but when trying to define a tick script of type batch with subqueries, we get an error.
The query we run:
`SELECT COUNT(DISTINCT(last)) FROM (SELECT LAST("version")  FROM "dbname"."autogen".measurement where time > now() - 120h GROUP BY "host") group by cluster`
The error:

> failed to parse InfluxQL query: found (, expected identifier at line 1, char 35

Start by reproducing the reported batch tick-script query and its InfluxQL parse error, then trace the tick script query-parsing entry point. Compare parsing of the outer query with the nested SELECT and verify that the supplied subquery is accepted without regressing existing query handling.

Written by the indexing model from the issue text.