Install pip requirements from pypi.openstack.org.

While `setup.py`s were being installed from the openstack
pypi mirror, `pip-requires` were coming from pypi.python.org,
which has been observed to be less stable.

This change installs all pip-requires via pypi.openstack.org.

Change-Id: Id78110232f1f6cbce63fbe02c63f30c0e1953212
Merge "Install pip requirements from pypi.openstack.org."