devstack: stop using USE_CONSTRAINTS and setup_package
devstack: stop using USE_CONSTRAINTS and setup_package

Change I843208e2e982eb04931b76f5cb4bd219fbcd70de in devstack removed the
usage of USE_CONSTRAINTS entirely without any warning. That means every
pip installed packaged is now forced to honor global requirements.

Now the gate is broken because the upper-constraint from
openstack/requirement build the wheel for pandas with the wrong version
etc. Since we just don't want to be bothered with that repository, we
have to bypass devstack usual setup function.

Change-Id: I4988f41e21c8efd15f3f619cff9abfd5fd39ea79

sileht/gnocchi,gnocchixyz/gnocchi,sileht/gnocchi,leandroreox/gnocchi,gnocchixyz/gnocchi,leandroreox/gnocchi