Instead of using the CA bundle, this sets HAProxy to use a specific file
for validating the certificates of the services it's proxying. This
helps in two ways:
* Improves performance since validation will check only one certificate.
* Improves security since we're only the certificates signed by one CA
are valid, instead of any certificate that the system trusts (which
could include potentially compromised public certs).
Change-Id: Id6de045b3c93c82d37e0b0657c17a3108516016a
82ff1acf03