Query returns just ERR if the subquery GROUPs BY both a time interval and a tag

[rossmcdonald]

Steps to reproduce:

1. Write some data

> insert giraffes,name=chrono leaves_consumed=12 1485298440000000000
> insert giraffes,name=graf leaves_consumed=8 1485298440000000000
> insert giraffes,name=chrono leaves_consumed=13 1485298445000000000
> insert giraffes,name=graf leaves_consumed=2 1485298445000000000
> insert giraffes,name=chrono leaves_consumed=15 1485298450000000000
> insert giraffes,name=graf leaves_consumed=4 1485298450000000000
> insert giraffes,name=chrono leaves_consumed=13 1485298455000000000
> insert giraffes,name=graf leaves_consumed=5 1485298455000000000

> select * from giraffes
name: giraffes
time                 leaves_consumed name
----                 --------------- ----
2017-01-24T22:54:00Z 12              chrono
2017-01-24T22:54:00Z 8               graf
2017-01-24T22:54:05Z 13              chrono
2017-01-24T22:54:05Z 2               graf
2017-01-24T22:54:10Z 15              chrono
2017-01-24T22:54:10Z 4               graf
2017-01-24T22:54:15Z 13              chrono
2017-01-24T22:54:15Z 5               graf

2. Run a query where the subquery's GROUP BY clause includes a time interval and tag

> SELECT * FROM (SELECT MEAN("leaves_consumed") FROM "giraffes" WHERE time >= '2017-01-24T22:54:00Z' AND time <= '2017-01-24T22:54:15Z' GROUP BY time(10m),"name")

ERR:

Expected behavior:

I'd expect to get either this:

name: giraffes
tags: name=chrono
time                 mean
----                 ----
2017-01-24T22:50:00Z 13.25

name: giraffes
tags: name=graf
time                 mean
----                 ----
2017-01-24T22:50:00Z 4.75

Or this:

name: giraffes
time                 mean   name
----                 ----   ----
2017-01-24T22:50:00Z 13.25  chrono
2017-01-24T22:50:00Z 4.75   graf

Actual behavior:

I get ERR:.

Pulled from #7875.

[jsternberg]

Fixed via #8051.