Update overview.rst
Update overview.rst

Update section related to Swift integration and usage. In the past it
wasn't clear if all needed features are implemented or not.

Change-Id: I48c5b5e33666ed391cf6b2869cd0f91f9fcfcf17

henaras/sahara,redhat-openstack/sahara,esikachev/sahara-backup,zhangjunli177/sahara,redhat-openstack/sahara,matips/iosr-2015,zhujzhuo/Sahara,bigfootproject/sahara,openstack/sahara,egafford/sahara,esikachev/sahara-backup,matips/iosr-2015,ekasitk/sahara,openstack/sahara,zhujzhuo/Sahara,ekasitk/sahara,zhangjunli177/sahara,bigfootproject/sahara,zhujzhuo/Sahara,crobby/sahara,redhat-openstack/sahara,crobby/sahara,henaras/sahara,esikachev/sahara-backup,crobby/sahara,matips/iosr-2015,tellesnobrega/sahara,henaras/sahara,tellesnobrega/sahara,zhangjunli177/sahara,bigfootproject/sahara,egafford/sahara,ekasitk/sahara