Add a workaround for octavia resources cleanup

So far, in case that Octavia loadbalancers (both amphora and ovn
providers) have had children (Octavia resources which were associated
to them), they couldn't have been deleted using the current tobiko
cleanup commands.

This patch adds to the cleanup commands the loadbalancer deletion
before the stacks are being deleted.

A seperate BZ (#2060338) was opened against openstack-heat for not
adding the --cascade option when deleting LBs with children.

Workarounds BZ #2060338 until it is fixed.

Change-Id: I58bfd7d1d63c6a028470b895d588d47fd9f0fcc2

roles/tobiko-cleanup/tasks/main.yaml

@@ -1,4 +1,11 @@
 ---
+- name: "cleanup Loadbalancers created by Tobiko tests"
+  shell: |
+    source {{ stackrc_file }}
+    openstack loadbalancer list -f value -c 'name' | \
+        grep "^tobiko\." | \
+        xargs -r openstack loadbalancer delete --cascade --wait
+  ignore_errors: yes
 
 - name: "cleanup Heat stacks created by Tobiko tests"
   shell: |