Bug 1846970

OSP16.1 with RHOS-16.1-RHEL-8-20200611.n.0 compose fails deployments with octavia in OSP-phase2.

Failure in /var/lib/mistral/overcloud/ansible.log can be seen as (shortened):

> TASK [octavia-controller-post-config : create ip list (remove the last two characters)] ***
> Friday 12 June 2020  21:35:08 -0400 (0:00:00.429)       0:02:56.431 ***********
> ok: [controller-0]
> ok: [controller-1]
> ok: [controller-2]
>  
> TASK [octavia-controller-post-config : create ip list (rsyslog)] ***************
> Friday 12 June 2020  21:35:08 -0400 (0:00:00.291)       0:02:56.723 ***********
> fatal: [controller-0]: FAILED! => {\"msg\": \"The conditional check 'enable_log_offloading | bool' failed. The error was: An unhandled exception occurred while templating '{{ enable_log_offloading }}'. Error was a <class 'ansible.errors.AnsibleError'>, original message: An unhandled exception occurred while templating '{{ enable_log_offloading }}'. Error was a <class 'ansible.errors.AnsibleError'>, original message: An unhandled exception occurred while templating '{{ ena
>  
> ... snip ...
>  
> og_offloading }}'. Error was a <class 'ansible.errors.AnsibleError'>, original message: An unhandled exception occurred while templating '{{ enable_log_offloading }}'. Error was a <class 'ansible.errors.AnsibleError'>, original message: An unhandled exception occurred while templating '{{ enable_log_offloading }}'. Error was a <class 'ansible.errors.AnsibleError'>, original message: An unhandled exception occurred while templating '{{ enable_log_offloading }}'. Error was a <class 'ansible.errors.AnsibleError'>, original message: An unhandled exception occurred while templating '{{ enable_log_offloading }}'. Error was a <class 'ansible.errors.AnsibleError'>, original message: recursive loop detected in template string: {{ enable_log_offloading }}\
> \
> The error appears to be in '/usr/share/ansible/roles/octavia-controller-post-config/tasks/main.yml': line 19, column 7, but may\
> be elsewhere in the file depending on the exact syntax problem.\
> \
> The offending line appears to be:\
> \
>   block:\
>     - name: create ip list (rsyslog)\
>       ^ here\
> \"}
>  
> // ... same repeats for other controllers like controller-1 and -2

With help from gthiemonge on irc:
- https://review.opendev.org/#/c/733712/ (tripleo-ansible) introduced this code part
- https://review.opendev.org/#/c/733710/  (tripleo-heat-templates) likely missing and so causing the issue
- while there is default value in role, its first referenced in playbook above
  it and so requires the value to be provided

Likely involved:
> tripleo-ansible.noarch                            0.5.1-0.20200611113654.34b8fcc.el8ost
> openstack-tripleo-heat-templates.noarch           11.3.2-0.20200608073443.f604618.el8ost