Slow log creation

```
$ time makelogs -c 300k -d 5
Generating 300000 events from 2015-06-19T00:00:00+00:00 to 2015-06-29T23:59:59+00:00
......................................................................................................

created 300000 events

real 16m19.699s
```

This is when running ES in a constrained vm, so the slowness it really amplified. In version 1.4.1 and previous, that would take a minute or 2 at most.