Use six to improve python 3 compatibility.
Use six to improve python 3 compatibility.

* StringIO

Change-Id: I8471e525566a0353d9276529be4b0d0e0cbf6cd6

tellesnobrega/storm_plugin,keedio/sahara,openstack/sahara,bigfootproject/sahara,zhujzhuo/Sahara,ekasitk/sahara,citrix-openstack-build/sahara,crobby/sahara,zhujzhuo/Sahara,rnirmal/savanna,tellesnobrega/sahara,crobby/sahara,esikachev/scenario,redhat-openstack/sahara,matips/iosr-2015,esikachev/sahara-backup,esikachev/scenario,matips/iosr-2015,tellesnobrega/storm_plugin,ekasitk/sahara,rnirmal/savanna,xme1226/sahara,redhat-openstack/sahara,egafford/sahara,tellesnobrega/sahara,zhangjunli177/sahara,henaras/sahara,henaras/sahara,mapr/sahara,esikachev/sahara-backup,xme1226/sahara,xme1226/sahara,citrix-openstack-build/sahara,henaras/sahara,ekasitk/sahara,zhujzhuo/Sahara,bigfootproject/sahara,tellesnobrega/storm_plugin,citrix-openstack-build/sahara,egafford/sahara,openstack/sahara,esikachev/sahara-backup,zhangjunli177/sahara,matips/iosr-2015,mapr/sahara,crobby/sahara,esikachev/scenario,redhat-openstack/sahara,mapr/sahara,keedio/sahara,keedio/sahara,bigfootproject/sahara,zhangjunli177/sahara