A new setuptools release has changed the way pip installs are done,
see [0]. With this change we switch back to using the distro
method for global pip installs.
Temporarily make grenade jobs non-voting in order to allow this
patch to be backported.
[0] http://lists.openstack.org/pipermail/openstack-discuss/2020-August/016905.html
Change-Id: I5d8aa0e58e0409c54451b51de5eb70ba9a68d849
(cherry picked from commit 18b4251bf4)