Force qemu-kvm-rhev on RHELs

Packstack should make sure that qemu-kvm-rhev (qemu-img-rhev) is installed
on RHEL, because Nova fails to create snapshot using qemu-img.

Change-Id: Ic3370301b5dc103758adcb15dd03cee6b5f284d7
Fixes: rhbz#1049861
Merge "Force qemu-kvm-rhev on RHELs"