The environment that Travis-CI sets up is somehow broken with regards
to the requirements for six.  The exact message we get and running
selftests/run is:

   pkg_resources.ContextualVersionConflict: (six 1.9.0
   (/home/travis/virtualenv/python3.4_with_system_site_packages/lib/python3.4/site-packages),
   Requirement.parse('six>=1.10.0'), {'Fabric3'})

Let's bump the requirements to 1.10.0, to try to help Travis-CI.
Signed-off-by: NCleber Rosa <crosa@redhat.com>