Mpack uses wrong group for owning HDFS directories

org.apache.hadoop.security.AccessControlException: Permission denied: user=storm, access=WRITE, inode="/apps/metron/indexing/indexed/snort/enrichment-null-0-0-1490305873514.json":metron:metron:drwxrwx

The group got changed a bit ago from cluster_env.user_group (hadoop) to cluster_env.metron_group (metron). However, because everything right now runs as the storm user (which is in the hadoop group), it doesn't have perms to write anymore.