Fix get/delete requests in Presto to accept headers

[toru-takahashi]

Add headers argument in get/delete requests with Presto.

Background

I would like to support Superset as BI tool to connect to Presto.
But, Presto I use requires X-Presto-User header to authenticate.
The current code seems to accept headers at only POST request.
Then, we couldn't pull data by using fetchall() and poll()

This fix accepts headers parameter into these functions.

(Dropbox CLA signed)

[shivarajugowda]

I also hit this problem lately and as @toru-takahashi mentioned passing the headers to GET calls(as done in the POST call) fixed the problem. Could we consider including the change? The older changes with the more recent tests might be causing the travis-ci errors. If needed I can clean up the fix and resubmit a pull request.

[bkyryliuk]

@shivarajugowda - please go for it. It also would be great to add some unit tests to the PR. Happy to review it.

[toru-takahashi]

Looks this issue has been fixed.
https://github.com/dropbox/PyHive/blob/master/pyhive/presto.py#L242-L247