Bind mount needed cert for haproxy

Bind mount needed cert for haproxy

haproxy needs the deployed SSL cert file to function when TLS is
enabled.

It is also required for the docker-puppet haproxy container since the
haproxy puppet module uses a validate_cmd to check the generated config
file is valid that fails when the required SSL cert is not present.
There is no clean way to disable this feature [1] so we need to bind
mount the cert into the container.

[1] https://github.com/puppetlabs/puppetlabs-haproxy/blob/4753ea5b2506ee093e9b4c8af6e91201d476d426/manifests/config.pp#L53-L57

Change-Id: Id2df144b678769def204961236624091d4e5c457