broker should exit if hitting exceptions durin startup; patched by Jun Rao; reviewed by Sriram Subramanian, Swapnil Ghike and Neha Narkhede; kafka-768

core/src/main/scala/kafka/server/KafkaServerStartable.scala

@@ -38,6 +38,7 @@ class KafkaServerStartable(val serverConfig: KafkaConfig) extends Logging {
       case e =>
         fatal("Fatal error during KafkaServerStable startup. Prepare to shutdown", e)
         shutdown()
+        System.exit(1)
     }
   }