ppc64le: Workaround for manylinux issue
ppc64le: Workaround for manylinux issue

Because of a discrepency in how ppc64le is referred to in distros,
we are hitting a bug in manylinux [0] that effects greenlet. This
patch clones greenlet-1.0.0 and modifies the centos-8.yaml vars
file in tripleo-ci so that it installs greenlet from source in
the venv_build virtual environment.

[0] https://github.com/pypa/manylinux/issues/687

Change-Id: Ie1f0f7928866e667982f33990ce312a16da93167

redhat-openstack/rdo-infra,redhat-openstack/rdo-infra,rdo-infra/ci-config,redhat-openstack/rdo-infra,redhat-openstack/rdo-infra,rdo-infra/ci-config,rdo-infra/ci-config,rdo-infra/ci-config