Update oslo-incubator threadgroup module
Update oslo-incubator threadgroup module

Changes -
 * Simple typo correction
 * threadgroup: use threading rather than greenthread

Change-Id: Ib7c8dc88e9a4a9936087cfe7938a213d95277fdc

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