Use ensure-pip for stackviz pip install
Use ensure-pip for stackviz pip install

Infra is trying to move to nodes that do not come with pip/virtualenv
pre-installed on the image; for details see the spec at [1].

zuul-jobs include ensure-pip [2] to provide pip dependencies; use that
before installing stackviz.  Note that if pip is installed this is a
noop.

[1] https://docs.opendev.org/opendev/infra-specs/latest/specs/cleanup-test-node-python.html
[2] https://zuul-ci.org/docs/zuul-jobs/python-roles.html#role-ensure-pip

Needed-By: https://review.opendev.org/723762
Change-Id: I24925ab8e885404da64a3ecfca3848041b6dfc05

cisco-openstack/tempest,openstack/tempest,cisco-openstack/tempest,openstack/tempest