RHEL6: tuned virtual-guest profile doesn't change a Amazon xvd disk elevator

Issue

• The Red Hat Enterprise Linux 6 Amazon systems, which are based on Xen hypervisors, don't have the disks elevators changed to deadline when applying the the virtual-guest tuned profile.
• The reverse is also true; trying to revert to the "default" profile doesn't brings the disk elevator back to CFQ, if it was changed manually.