mirror-python33 failure

Noticed today when releasing oslo.messaging:

  https://jenkins.openstack.org/job/post-mirror-python33/319/console

2014-02-06 10:41:52.699 | File "/usr/local/lib/python2.7/dist-packages/pypi_mirror/cmd/run_mirror.py", line 255, in build_mirror
2014-02-06 10:41:52.700 | extra_search_dir=pip_cache_dir, venv_dir=venv))
2014-02-06 10:41:52.700 | File "/usr/local/lib/python2.7/dist-packages/pypi_mirror/cmd/run_mirror.py", line 108, in run_command
2014-02-06 10:41:52.701 | stderr=subprocess.STDOUT)
2014-02-06 10:41:52.701 | File "/usr/lib/python2.7/subprocess.py", line 679, in __init__
2014-02-06 10:41:52.702 | errread, errwrite)
2014-02-06 10:41:52.702 | File "/usr/lib/python2.7/subprocess.py", line 1249, in _execute_child
2014-02-06 10:41:52.702 | raise child_exception
2014-02-06 10:41:52.703 | OSError: [Errno 2] No such file or directory

This is the bit that's failing AFAICT

        venv_format = (
            "virtualenv --clear --extra-search-dir=%(extra_search_dir)s"
            " %(venv_dir)s")

                    self.run_command(
                        venv_format % dict(
                            extra_search_dir=pip_cache_dir, venv_dir=venv))