build-wheel-cache: Don't use virtualenv on python3 platforms

As noted inline, platforms are starting to decide to deprecate
virtualenv for "python3 -m venv".  Put in logic to use venv in our
Python 3 paths.

Change-Id: I46778642647d7be995d476fb567a9943cae66b8f

roles/build-wheel-cache/files/wheel-build.sh

@@ -8,6 +8,15 @@ LOGS=$(pwd)/logs
 
 FAIL_LOG=${LOGS}/failed.txt
 
+# NOTE(ianw) : Some Python 3 platforms (>= 9-stream) are deprecating
+# virtualenv.  When we finally ditch Python 2 platforms, just use
+# python3 -m venv everywhere.
+if [[ ${PYTHON_VERSION} =~ python2 ]]; then
+    VIRTUALENV_CMD="virtualenv -p $PYTHON_VERSION"
+else
+    VIRTUALENV_CMD="${PYTHON_VERSION} -m venv"
+fi
+
 # preclean logs
 mkdir -p ${LOGS}
 rm -rf ${LOGS}/*
@@ -44,7 +53,7 @@ for BRANCH in master $BRANCHES; do
     # setup the building virtualenv.  We want to freshen this for each
     # branch.
     rm -rf build_env
-    virtualenv -p $PYTHON_VERSION build_env
+    ${VIRTUALENV_CMD} build_env
 
     build_env/bin/pip install --upgrade pip
 

roles/build-wheel-cache/tasks/main.yaml

@@ -1,6 +1,15 @@
 - name: Ensure virtualenv dependency
   include_role:
     name: ensure-virtualenv
+  when: wheel_python == "python2"
+
+# NOTE(ianw) : 2022-02-08 - on python3 we use -m venv; ensure-pip will
+# set this up for us.  Remove above and the conditional here when we
+# drop python2 platforms.
+- name: Ensure pip
+  include_role:
+    name: ensure-pip
+  when: wheel_python == "python3"
 
 - name: Ensure wheel dir exists
   file: