diskimage-create check for qemu-kvm-ev/qemu-img-ev for CentOS
diskimage-create check for qemu-kvm-ev/qemu-img-ev for CentOS

Checking packages using "yum list installed qemu-kvm/qemu-img" fails for
Centos,while qemu-kvm-ev and qemu-img-ev are installed using
"RDO CentOS-7 - QEMU EV".

This repository is added by devstack.

I changed the shell script to check [qemu-kvm qemu-img] and [kpartx git]
separately and when [qemu-kvm qemu-img] are not found, check for
qemu-kvm-ev or qemu-img-ev instead of exiting.

Change-Id: I5bd929e5aba76319cc86e0fc97825929e32629c2
Close-Bug: #1637435

openstack/octavia,openstack/octavia,openstack/octavia