Move tempest plugin install to the end

For the tempest plugin install inside the tox venv to hold we need to
ensure that it's the last thing run that touches the tox venv before
devstack ends. Otherwise there is a chance we'll recreate the venv in
a later step of installing and configuring tempest. This commit
moves the plugin installation into it's own function and calls that
function as last phase of the tempest setup to make sure it runs last.

Change-Id: Ie253171537e8c5a9887cc30aba1cad4b31e57663

extras.d/80-tempest.sh

@@ -13,6 +13,8 @@ if is_service_enabled tempest; then
     elif [[ "$1" == "stack" && "$2" == "extra" ]]; then
         echo_summary "Initializing Tempest"
         configure_tempest
+        echo_summary "Installing Tempest Plugins"
+        install_tempest_plugins
     elif [[ "$1" == "stack" && "$2" == "post-extra" ]]; then
         # local.conf Tempest option overrides
         :

lib/tempest

@@ -600,6 +600,12 @@ function install_tempest {
     # running pip install -U on tempest requirements
     $TEMPEST_DIR/.tox/tempest/bin/pip install -c $REQUIREMENTS_DIR/upper-constraints.txt -r requirements.txt
     PROJECT_VENV["tempest"]=${TEMPEST_DIR}/.tox/tempest
+    popd
+}
+
+# install_tempest_plugins() - Install any specified plugins into the tempest venv
+function install_tempest_plugins {
+    pushd $TEMPEST_DIR
     if [[ $TEMPEST_PLUGINS != 0 ]] ; then
         tox -evenv-tempest -- pip install $TEMPEST_PLUGINS
         echo "Checking installed Tempest plugins:"