Fix image build after release of cryptography 3.4

Image build job fails with:
ModuleNotFoundError: No module named 'setuptools_rust'

This error appeared following the release of cryptography 3.4, which now
includes Rust code. It can be installed without Rust using a Python
wheel, but only with more recent pip than version 9.0.3 available as RPM
on CentOS 8. The cryptography bug report [1] recommends pip>=19.1.1.

[1] https://github.com/pyca/cryptography/issues/5753
Closes-Bug: #1915101
Change-Id: I7f4f3f0f90187ec86534cdc61b8c88b079552810

roles/oooci-build-images/tasks/pre.yaml

@@ -62,6 +62,12 @@
   become: true
   when: python_v == "py2"
 
+- name: Ensure a recent version of pip is installed
+  pip:
+    name: "pip>=19.1.1"
+    virtualenv: "{{ workspace }}/venv"
+    virtualenv_command: "/usr/bin/python3 -m venv"
+
 - name: Install deps from upper-constraints
   when: ansible_distribution == 'CentOS'
   pip: