Convert testmatrix run to venv

As part of our efforts to ship bare nodes, we want to install as
little as possible in any sort of pre-run jobs.  Since all infra nodes
have python3 available, use venv to create this small environment for
the test matrix production, and avoid having to pull in any other
dependencies.

Change-Id: Ie8b09ab60841f9d1b15ae1a7afec51906cd89f95

roles/test-matrix/tasks/main.yaml

@@ -3,23 +3,23 @@
     src: "{{ test_matrix_features }}"
     dest: "{{ ansible_user_dir }}"
 
-- name: Check for virtualenv
-  command: which virtualenv
+- name: Check for venv
+  command: python3 -m venv -h
   changed_when: false
   failed_when: false
-  register: virtualenv_available
+  register: venv_available
 
-- name: Ensure virtualenv is installed
+- name: Ensure venv
   fail:
-    msg: "Please ensure virtualenv is available!"
+    msg: Can not find venv module?
   when:
-    - virtualenv_available.rc != 0
-    - ansible_os_family != 'Darwin'
+    - venv_available.rc != 0
 
-- name: Install PyYAML to parse the test matrix
-  pip:
-    name: PyYAML
-    virtualenv: "/tmp/.test_matrix_venv"
+- name: Create testmatrix venv
+  command: python3 -m venv /tmp/.test_matrix_venv
+
+- name: Install PyYAML to venv
+  command: /tmp/.test_matrix_venv/bin/pip install PyYAML
 
 - name: Append neutron to configs for stable/ocata+
   set_fact: