Add guest image customization to DevStack plugin.

CI jobs for this plugin use DevStack to install and configure
OpenStack and to upload guest images to be used for tests.

This change allow to customize guest images just before
being sent to image service with the purpose of installing
new packages (like socat), configuring N network devices, etc.

This change has been created because for testing multicast
socat is required, but it was designed with the idea
of being used to allow further guest images customizations.

Change-Id: I88491dbb65031fe3743d1c3d27c38a57b5511794
diff --git a/devstack/plugin.sh b/devstack/plugin.sh
index a2009ea..e7e30a9 100644
--- a/devstack/plugin.sh
+++ b/devstack/plugin.sh
@@ -1,6 +1,12 @@
+# Directory where this plugin.sh file is
+NEUTRON_TEMPEST_PLUGIN_DIR=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
+
+source "${NEUTRON_TEMPEST_PLUGIN_DIR}/customize_image.sh"
+
 # install_neutron_tempest_plugin
 function install_neutron_tempest_plugin {
     setup_dev_lib "neutron-tempest-plugin"
+    install_customize_image_tools
 }
 
 if [[ "$1" == "stack" ]]; then