Changes to perform rolling restart of HDFS datanode

Refer #194. The changes are to perform rolling restart if HDFS datanode service.Also there are HDFS datanode related changes for #309, #305 & #183.    
Will it be a better idea to put number of tries/time period value instead of just a static message? Something similar to [this](https://github.com/amithkanand/chef-bcpc/blob/hadoop_hortonworks/cookbooks/kafka-bcpc/recipes/kafka.rb#L25-25)