Update _system_tuning.rb
Update _system_tuning.rb

Fix a nasty bug when transparent hugepage file does NOT exist

    root@hadoop-yarnresourcemgr-0:~# ohai platform_family          [
      "debian"
    ]
    root@hadoop-yarnresourcemgr-0:~# ls /sys/kernel/mm/transparent_hugepage/defr
    ls: cannot access /sys/kernel/mm/transparent_hugepage/defrag: No such file o

    [2015-04-04T00:16:55+00:00] ERROR: execute[disable-transparent-hugepage-comp
    ---- Begin output of echo never > /sys/kernel/mm/transparent_hugepage/defrag
    STDOUT:
    STDERR: sh: 1: cannot create /sys/kernel/mm/transparent_hugepage/defrag: Dir
    ---- End output of echo never > /sys/kernel/mm/transparent_hugepage/defrag -
    Ran echo never > /sys/kernel/mm/transparent_hugepage/defrag returned 2
    [2015-04-04T00:16:55+00:00] FATAL: Chef::Exceptions::ChildConvergeError: Che
cdapio/hadoop_cookbook,cdapio/hadoop_cookbook,caskdata/hadoop_cookbook,caskdata/hadoop_cookbook,cdapio/hadoop_cookbook,caskdata/hadoop_cookbook