Force "yes" in command prompt when using "pip uninstall"

[Rodolfo Alonso]

With https://review.openstack.org/#/c/463216/, libvirt-python is uninstalled and installed to handle potential upgrades.

The problem arises during the uninstallation. The command "sudo -H pip uninstall libvirt-python" asks for interactive confirmation.

Because there is no "force" option in pip uninstall, the following solution is proposed:
  /usr/bin/yes | sudo -H pip uninstall libvirt-python

Manual execution log:
[stack@silpixa00394062 ~]$sudo -EH pip uninstall libvirt-python
DEPRECATION: Uninstalling a distutils installed project (libvirt-python) has been deprecated and will be removed in a future version. This is due to the fact that uninstalling a distutils project will only partially uninstall the project.
Uninstalling libvirt-python-3.0.0:
  /usr/lib/python2.7/dist-packages/libvirt_python-3.0.0.egg-info
Proceed (y/n)?

[Rodolfo Alonso (rodolfo-alonso-hernandez)]

Duplicated: https://bugs.launchpad.net/devstack/+bug/1691172