"python setup.py --help-commands" fails

Here's the log of a session that reproduces the error.

stefanesmacbook% mkvirtualenv pbr
New python executable in pbr/bin/python2.7
Also creating executable in pbr/bin/python
Installing setuptools, pip...done.

(pbr)stefanesmacbook% pip install pbr
Collecting pbr
  Using cached pbr-0.10.7-py2.py3-none-any.whl
Requirement already satisfied (use --upgrade to upgrade): pip in /Users/fermigier/envs/pbr/lib/python2.7/site-packages (from pbr)
Installing collected packages: pbr

Successfully installed pbr-0.10.7

(pbr)stefanesmacbook% cat setup.py
from setuptools import setup

setup(setup_requires=['pbr'], pbr=True)

(pbr)stefanesmacbook% cat setup.cfg
[metadata]
name = test

(pbr)stefanesmacbook% python setup.py --help-commands
Traceback (most recent call last):
  File "setup.py", line 3, in <module>
    setup(setup_requires=['pbr'], pbr=True)
  File "/usr/local/Cellar/python/2.7.9/Frameworks/Python.framework/Versions/2.7/lib/python2.7/distutils/core.py", line 137, in setup
    ok = dist.parse_command_line()
  File "/Users/fermigier/envs/pbr/lib/python2.7/site-packages/setuptools/dist.py", line 298, in parse_command_line
    result = _Distribution.parse_command_line(self)
  File "/usr/local/Cellar/python/2.7.9/Frameworks/Python.framework/Versions/2.7/lib/python2.7/distutils/dist.py", line 464, in parse_command_line
    if self.handle_display_options(option_order):
  File "/Users/fermigier/envs/pbr/lib/python2.7/site-packages/setuptools/dist.py", line 678, in handle_display_options
    return _Distribution.handle_display_options(self, option_order)
  File "/usr/local/Cellar/python/2.7.9/Frameworks/Python.framework/Versions/2.7/lib/python2.7/distutils/dist.py", line 669, in handle_display_options
    self.print_commands()
  File "/Users/fermigier/envs/pbr/lib/python2.7/site-packages/setuptools/dist.py", line 438, in print_commands
    cmdclass = ep._load()
  File "/Users/fermigier/envs/pbr/lib/python2.7/site-packages/pkg_resources/__init__.py", line 2268, in _load
    module = __import__(self.module_name, fromlist=['__name__'], level=0)
  File "/Users/fermigier/envs/pbr/lib/python2.7/site-packages/pbr/testr_command.py", line 47, in <module>
    from testrepository import commands
ImportError: No module named testrepository