Require a CA Cert in a SecurityCreds object and via SSL

The initial version of security would allow a CA Certificate, but would not require one.  Now when using a `SecurityCreds` object you must supply a CA Cert.  This CA Cert option can now also be a list of cert files.

At the library level, OpenSSL will now verify the peer certificate (from the server) with the list of CA certs cached on the client.