Fix error when system uses /usr/bin/qemu-kvm, as in CentOS 7.2.
Fix error when system uses /usr/bin/qemu-kvm, as in CentOS 7.2.

Got "libvirt.libvirtError" error when using "/usr/bin/qemu-kvm" on CentOS7.2.
CentOS 7.2 uses "/usr/libexec/qemu-kvm", this patch fixes it.

Change-Id: Icf2951701fddfac8e2f0641f6f555adb8a3c185b
Closes-Bug: #1649449

SauloAislan/ironic,openstack/ironic,openstack/ironic,pshchelo/ironic,NaohiroTamura/ironic,NaohiroTamura/ironic,pshchelo/ironic,SauloAislan/ironic