InfluxDB query can't be parsed by kapacitor

Surprisingly a query which works just fine in influxdb fails in kapacitor:
```
var test = batch
|query('''
SELECT non_negative_difference(mean("value")) AS "diff"
FROM "telegraf"."autogen"."test"
''')
.period(5m)
.every(1m)
.groupBy(time(5m), *)
```
Results in:
```
`failed to parse InfluxQL query: expected field argument in non_negative_difference()`
```

Reproduce the reported Kapacitor batch query and compare its parsing of non_negative_difference(mean("value")) with the equivalent query accepted by InfluxDB. Locate the InfluxQL parsing path, then add coverage for the reported query and verify that it parses successfully without breaking existing function handling.

Written by the indexing model from the issue text.