Fix issues caused by HttpRequest API change in Python 3
Fix issues caused by HttpRequest API change in Python 3

Python 3's urllib changed the request object so that instead of having a
`get_data` method, there's now just a `data` attribute. It turns out
that this attribute also existed in Python 2, although it wasn't the
official API. This change modifies the idonethis tests to use that
everywhere.

Testing Done:
Ran rbintegrations unit tests.

Reviewed at https://reviews.reviewboard.org/r/10922/

reviewboard/rbintegrations,reviewboard/rbintegrations,reviewboard/rbintegrations