[MINOR] [CORE] Allow History Server to read kerberos opts from config file.

Order of initialization code was wrong.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #5998 from vanzin/hs-conf-fix and squashes the following commits:

00b6b6b [Marcelo Vanzin] [minor] [core] Allow History Server to read kerberos opts from config file.

core/src/main/scala/org/apache/spark/deploy/history/HistoryServer.scala

@@ -203,8 +203,8 @@ object HistoryServer extends Logging {
 
   def main(argStrings: Array[String]) {
     SignalLogger.register(log)
-    initSecurity()
     new HistoryServerArguments(conf, argStrings)
+    initSecurity()
     val securityManager = new SecurityManager(conf)
 
     val providerName = conf.getOption("spark.history.provider")