* modified preseed/bigtop-init
   - [FIX] YARN NodeManager needs /var/log/hadoop-yarn/apps
     folder on HDFS. Default user needs /user/user on HDFS.
     We need to configure the right permission with `hdfs'
     system account for HDFS due to security issue.
 * modified preseed/bigtop.seed
   - add w3m package for browsing status.
     Note: http://localhost:50070 for NameNode (HDFS)
           http://localhost:8088  for YARN ResourceManager