Fix certification task instructions
Fix certification task instructions

Replacing incorrect usage of "Task" with "To"

Change-Id: I8dc25c938091e8a821959e1e3faf173c720de4a5

openstack/rally,vganapath/rally,yeming233/rally,openstack/rally,vganapath/rally,vganapath/rally,vganapath/rally,openstack/rally,yeming233/rally,openstack/rally