2.0.0-alpha19: Mapped variables use the key instead of the mapped value in queries

[ginoledesma]

Steps to reproduce:

1. Create a new variable called Resolution of type map. For example, using the CSV format:

a.10 seconds,"10s"
b.30 seconds,"30s"

2. Create a Flux query that references this variable

from(bucket: "telegraf")
  |> range(start: v.timeRangeStart, stop: v.timeRangeStop)
  |> filter(fn: (r) => r._measurement == "cpu")
  |> filter(fn: (r) => r._field == "usage_user")
  |> filter(fn: (r) => r.cpu == "cpu-total")
  |> map(fn: (r) => ({r with _variable: v.Resolution}))

3. View the results using the Raw Data format

Expected behavior:
The _variable field should display the mapped value (10s)

Actual behavior:
The _variable field shows the key of the variable (a.10 seconds)

Environment info:

• System info: Linux 4.15.0-1052-aws x86_64
• InfluxDB version: 2.0.0-alpha.19 ce3e296 2019-10-30T23:33:54Z

[ginoledesma]

Bug still present in 2.0.0-alpha20 and 2.0.0-alpha21

[asalem1]

Duplicate of #17026 - fixed in this PR:

#17072