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
Why lazy if you're using it in the next few lines anyway? Also, shouldn't this be keyed off some option? Some people won't want to disable cert verification.