Improve context.set_ctx to not fail
Improve context.set_ctx to not fail

* it will now not fail in case of trying to delete empty ctx

Change-Id: I564819ac942c8f611fade73c7915c73aa3b0aeea

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