SPARK-3883 SSL support for HttpServer and Akka

 - Introduced SSLOptions object
 - SSLOptions is created by SecurityManager
 - SSLOptions configures Akka and Jetty to use SSL
 - SSLOptions uses property file which is node-local to set SSL settings
 - Provided utility methods to determine the proper Akka protocol for Akka requests and to configure SSL socket factory for URL connections
 - Added tests cases for AkkaUtils, FileServer, SSLOptions and SecurityManager
Shouldn't this be a list? I'm pretty sure it's allowed to have multiple protocols enabled.

Also, given POODLE, it's probably a good idea to expose the setting to disable specific protocols, and have it include "SSLv3" by default.