Because enterprises tend to move very slowly, we're keeping Python 2.7

compatibility for RBTools 3.0. Two issues had snuck in that were

breaking this:

We had renamed uses of assertRaisesRegexp to use the new

assertRaisesRegex name. Unfortunately, this new name is only Python

   3.1+. I've changed it back, and made two uses of it instead call the

   more appropriate assertRaisesMessage helper, so now there's only

   one place that hits it.
The tqdm library depends on importlib_resources. Unfortunately,

   while tqdm is maintaining Python 2.7 compatibility, the newer

   versions of its dependency are not. I've added a pin for the last

   compatible version.

Ran setup.py develop under Python 2.7, and then ran all unit tests.