SSL support depends on whatever the C driver was compiled with. We should offer C++11 driver users the ability to specify their desired SSL support at configuration time. E.g.:

• Yes: use SSL, error if underlying C driver does not offer it
• No: Don't use SSL, even if underlying C driver does offer it
• Auto: SSL if C driver SSL.

See https://github.com/mongodb/mongo-cxx-driver/pull/400#discussion_r47811488 for motivation