Points with different time format won't join

Nobody has claimed this yet.

**OS:** RHEL 6 and 7 x64
**Reproduced in** Kapacitor 1.4 and 1.5
pre-built package (rpm)

The problem may not be specific only to join node, but it is a good case to demonstrate.
Some nodes (probably all InfluxQL nodes) changing time format when applied, from UTC to local, if used without ".usePointTimes" property.
And if i want later, in example, join streams with different time format - they never join, despite tags and time of points actually the same.

Here is sample synthetic script
```
dbrp "telegraf"."autogen"

var s1= batch
|query('SELECT mean("usage_idle") as usage FROM "telegraf"."autogen"."cpu"')
.period(1h)
.every(5s).align()
.groupBy('host','cpu')
|last('usage')
|httpOut('last')

var s2= batch
|query('SELECT mean("usage_idle") as usage FROM "telegraf"."autogen"."cpu"')
.period(10m)
.every(5s).align()
.groupBy('host','cpu')
|last('usage')
|last('last').usePointTimes()
|httpOut('lastp')
s1
|join(s2)
.as('s1','s2')
.tolerance(1m)
|httpOut('join')
```
outputs:
**s1**
```series: [
{
name:"cpu",
tags:{
cpu:"cpu-total",
host:"host-a"
},
columns:[
"time",
"last"
],
values:[
[
"2018-10-26T11:36:10+03:00",
95.12228799820839
]
]
},
...
```

**s2**
```series: [
{
name:"cpu",
tags:{
cpu:"cpu-total",
host:"host-a"
},
columns:[
"time",
"last"
],
values:[
[
"2018-10-26T08:36:10Z",
96.05253758127586
]
]
},
...
```

**join**
```
{
series: null
}
```

Start with the supplied TICKscript and reproduce the mismatch between the s1 and s2 timestamps before the join. Inspect how equivalent UTC and local-offset times are compared, and consider the issue complete when the reproduced streams join correctly with coverage for this timestamp case.

Written by the indexing model from the issue text.