Use python3 venv instead of virtualenv

tempest-tox-plugin-sanity-check job is failing due to missing virtualenv.
As the job is running on master only and we don't support python2 anymore,
this patch edits the tempest-plugin-sanity.sh script so that it uses
python3 venv module to create a venv.

Change-Id: I3f711ec97ad9006c715bb45db9d8dd9d951bb6a1

tools/generate-tempest-plugins-list.py

@@ -52,6 +52,8 @@ BLACKLIST = [
     'x/tap-as-a-service',  # To avoid sanity-job failure
     'x/valet',  # https://review.opendev.org/#/c/638339/
     'x/kingbird',  # https://bugs.launchpad.net/kingbird/+bug/1869722
+    # vmware-nsx is blacklisted since https://review.opendev.org/#/c/736952
+    'x/vmware-nsx-tempest-plugin',
 ]
 
 url = 'https://review.opendev.org/projects/'

tools/tempest-plugin-sanity.sh

@@ -66,7 +66,7 @@ DEPS="-c${TOX_CONSTRAINTS_FILE}"
 # function to create virtualenv to perform sanity operation
 function prepare_workspace {
     SANITY_DIR=$(pwd)
-    virtualenv -p python3 --clear "$SANITY_DIR"/.venv
+    python3 -m venv "$SANITY_DIR"/.venv
     export TVENV="$SANITY_DIR/tools/with_venv.sh"
     cd "$SANITY_DIR"