Ability to generate haproxy config with the frontend/backend
sections rather than the old listen section. This allows
the generation of complex configs, such as for example giving
priority to local backends when routing traffic.
Make the new syntax configurable via a new hiera key
`haproxy_backend_syntax`. The frontend and backend config of
each service can be further tweaked via additional keys
tripleo::haproxy::<service>::frontend_options and
tripleo::haproxy::<service>::backend_options
By default, keep the current 'listen' syntax.
Tested with capability disabled, the haproxy config generated
for undercloud and ha overcloud doesn't change.
Tested with capability enabled, tempest smoke test passed.
Closes-Bug: #1941617
Change-Id: Ieb36f90c6709934aa3aa6668d3929bff872c30f5
7a6c5281e0