Copy Nova's workaround for RHEL6 eventlet issue

The eventlet on PyPI basically doesn't work on RHEL because we (Red Hat)
screwed up by not taking monkey patching into account when backporting
an API from python 3. This is the series of events:

  1) We backported a patch to RHEL6 from Python 3 which added an
     optional 'timeout' argument to subprocess.Popen:

       http://pkgs.devel.redhat.com/cgit/rpms/python/commit/?h=rhel-6.3&id=fc9a3f0e07

     This might sound innocuous but it means the wait() function get
     called with a timeout argument

  2) eventlet overrides this function, but doesn't know about the
     timeout argument, so it fails. To reproduce, try applying this to
     your python 2.7:

       https://gist.github.com/markmc/5500967

  3) eventlet doesn't yet support Python 3, so the only time this issue
     crops up is if you use eventlet on RHEL6

  4) We've fixed eventlet in EPEL6, but the issue still remains if you
     install eventlet from upstream

  5) Dave Malcolm sent a pull request to eventlet, but it has stalled:

       https://bitbucket.org/eventlet/eventlet/pull-request/30/add-dummy-timeout-parameter-to

Nova has long had a nasty workaround to patch eventlet in our virtualenv
and we now need this workaround in oslo-incubator to test processutils.
Let's add it here and make nova sync it from oslo-incubator.

I really hope we can get eventlet upstream "fixed" and the fix released
soon. When that happens, we can kill all this nastiness.

Change-Id: I62ce43a330d7ae94eda4c7498782a655e63747fa
Merge "Copy Nova's workaround for RHEL6 eventlet issue"