BUG: Avoid flaky usecols set in C engine
Explanation of the bug can be found <a href="https://github.com/pandas-dev/pandas/issues/14792#issuecomment-269115098">here</a>.

Closes #14792.

## [Current coverage](https://codecov.io/gh/pandas-dev/pandas/pull/14984?src=pr) is 84.78% (diff: 100%)
> Merging [#14984](https://codecov.io/gh/pandas-dev/pandas/pull/14984?src=pr) into [master](https://codecov.io/gh/pandas-dev/pandas/branch/master?src=pr) will increase coverage by **<.01%**

```diff
@@             master     #14984   diff @@
==========================================
  Files           145        145          
  Lines         51090      51094     +4   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits          43315      43319     +4   
  Misses         7775       7775          
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last update [7f0eefc...82cf55b](https://codecov.io/gh/pandas-dev/pandas/compare/7f0eefc2f81d6b34f252a5da38d31e515c295106...82cf55b1bd1ba8ec4f29a36458bd75aa361810e3?src=pr) @jreback , @jorisvandenbossche : Addressed comments, and everything is green. ok thanks @gfyoung 

