Add iptables-based active/standby scenario test

This patch adds a tempest scenario test for active/standby topology.

This scenario takes a similar approach to scenario proposed in Change-Id
Ibcd5552a67cea650edc72bfaa986357267ca2407 with the difference that it
does not rely on amphora stats API. Instead, it uses iptables to log VIP
traffic and make assertions based on logging.

Co-Authored-By: Michael Johnson <johnsomor@gmail.com>

Change-Id: I24a6fc3387166ec6cdbd57a5ca9f63743748ec68
diff --git a/playbooks/act_stby_iptables/pre.yaml b/playbooks/act_stby_iptables/pre.yaml
new file mode 100644
index 0000000..179569a
--- /dev/null
+++ b/playbooks/act_stby_iptables/pre.yaml
@@ -0,0 +1,16 @@
+# Tempest runs under an unpriviledged user, thus the user cannot read
+# /etc/octavia/.ssh/ created by the Octavia devstack plugin. As work-around,
+# a new SSH key is generated and given read access to all users.
+# See also OCTAVIA_USE_PREGENERATED_SSH_KEY and
+# OCTAVIA_PREGENERATED_SSH_KEY_PATH set in the
+# octavia-v2-act-stdby-dsvm-scenario job definition
+- hosts: all
+  name: Octavia DSVM jobs pre-run playbook
+  tasks:
+    - name: Generate Octavia RSA key
+      shell: ssh-keygen -t rsa -f /tmp/octavia_ssh_key -q -N ""
+    - name: Allow read permissions to other users
+      file:
+        path: /tmp/octavia_ssh_key
+        state: file
+        mode: 0644