ssl.ca_certs should be supported in authentication.conf

[Vincent Ladeuil]

We currently handle ssl cert verification via two options that are only queried from bazaar.conf.

That makes 'optional' for ssl.ca_certs = 'optional' complex to support.

Having the ability to specify these options in authentication.conf per-host will allow one to disable the verification for hosts that don't provide certificates which is what 'optional' is about (it makes little sense to check that ssl.ca_certs is a valid path if we don't intent to verify the host certificate anyway).

[Vincent Ladeuil (vila)]

This will also allow to support self-signed certificates more easily by allowing ssl.ca_certs to point to the server certificate.