cannot pass tests on VizCluster after this merge

[fouriaux]

I got the following error message:

test_process_not_found (tests.toolbox.test_process.TestFindExecutable) ... passed
Failure: ImportError (No module named extern) ... ERROR
Failure: ImportError (No module named extern) ... ERROR
Failure: ImportError (No module named extern) ... ERROR
======================================================================
1) ERROR: Failure: ImportError (No module named extern)
----------------------------------------------------------------------
   Traceback (most recent call last):
    .tox/py27/lib/python2.7/site-packages/nose/loader.py line 418 in loadTestsFromName
      addr.filename, addr.module)
    .tox/py27/lib/python2.7/site-packages/nose/importer.py line 47 in importFromPath
      return self.importFromDir(dir_path, fqname)
    .tox/py27/lib/python2.7/site-packages/nose/importer.py line 94 in importFromDir
      mod = load_module(part_fqname, fh, filename, desc)
    tests/benchmark/benchmark.py line 13 in <module>
      from hpcbench.driver import YAML_REPORT_FILE, MetricsDriver
    hpcbench/driver.py line 25 in <module>
      from . campaign import from_file
    hpcbench/campaign.py line 8 in <module>
      from pkg_resources.extern import packaging
   ImportError: No module named extern