Fix aggregator window and shutdown of multiple aggregators

[danielnelson]

closes #5637
closes #5595

Required for all PRs:

• Signed CLA.
• Associated README.md updated.
• Has appropriate unit tests.

[danielnelson]

@toni-moreno @sbengo Here are some builds with the aggregator fix, would be very appreciated if you could try them out.

• telegraf-1.11.0~e48ee92e-0.x86_64.rpm
• telegraf_1.11.0~e48ee92e-0_amd64.deb

[sbengo]

Hi @danielnelson , thanks the PR!

I have been testing on the RH and it seems that it is giving OK results.

I have done 2 test on our RH 7.5 VM:

• A - based on file input described in: Basicstats counter not working as expected #5595 (comment)
• B - based on tail input described in: Basicstats counter not working as expected #5595 (comment) and Basicstats counter not working as expected #5595 (comment)

A - File input

> select sum(resp_time_count) from apachelog2 where time > now() - 4h group by time(1m),request
name: apachelog2
tags: request=/200_1sec.php
time                sum
----                ---
1553845260000000000 60
1553845320000000000 60
1553845380000000000 60
1553845440000000000 60

name: apachelog2
tags: request=/200_2sec.php
time                sum
----                ---
1553845260000000000 30
1553845320000000000 30
1553845380000000000 30
1553845440000000000 30

B - Original tail with tag routing

> select sum(resp_time_count) from apachelog2 where time > now() - 4m group by time(1m),request
name: apachelog2
tags: request=/200_1sec.php
time                sum
----                ---
1553852760000000000
1553852820000000000 60
1553852880000000000 60
1553852940000000000 60
1553853000000000000 60

name: apachelog2
tags: request=/200_2sec.php
time                sum
----                ---
1553852760000000000
1553852820000000000 30
1553852880000000000 30
1553852940000000000 30
1553853000000000000 30

More info:

Dropped metrics are 0 now (expected behaviour):

> select non_negative_derivative(last(metrics_dropped),1m) from "internal_aggregate" where time  > now() - 4m group by time(1m);
name: internal_aggregate
time                non_negative_derivative
----                -----------------------
1553852820000000000 0
1553852880000000000 0
1553852940000000000 0
1553853000000000000 0