added capath option to curl Downloader

Hi

In my company, we use some repositories which are signed by a private CA. The cert of the CA is installed on every server in /etc/ssl/certs, rather than added to a bundle.

I think it may be valuable to have an option which permit to use such a certs dir for the CA, when adding a box. Currently, only the cacert option could be passed to the Downloader component, my patch adds the support to the --capath option of curl.

Hope you will merge it.

Regards,