Install setuptools<8.0

New setuptools (>=8.0) breaks with versions used in older versions of
things. Specifically .gshortsha1 source identifiers do not parse and are
sorted as coming before all other versions. Using <8.0 at least unwedges
us then we can work on backporting changes to use newer pbr which will
use +gshortsha1 which sorts properly.

Change-Id: Iae98d9d7e97b81955cafe1b88022133e6902e551
Merge branch 'stable/icehouse' of https://github.com/openstack-dev/devstack into stable/icehouse