Add devstack plugin support

Instead of requiring users to install the plugin manually, add a
devstack plugin that can be enabled in order to perform the
installation.

Change-Id: I3015dbc204ea3e4cd2592c03bbda3d398f4d050a
diff --git a/devstack/plugin.sh b/devstack/plugin.sh
new file mode 100644
index 0000000..babf033
--- /dev/null
+++ b/devstack/plugin.sh
@@ -0,0 +1,14 @@
+
+# install_octavia_tempest_plugin
+function install_octavia_tempest_plugin {
+    setup_dev_lib "octavia-tempest-plugin"
+}
+
+if [[ "$1" == "stack" ]]; then
+    case "$2" in
+        install)
+            echo_summary "Installing octavia-tempest-plugin"
+            install_octavia_tempest_plugin
+            ;;
+    esac
+fi