Support for libvirt/QEMU tar releases

Enable to install libvirt and QEMU from tar releases.
The definition of the variables LIBVIRT_VERSION and QEMU_VERSION
will result in the compilation and the installation of libvirt and
QEMU from the tar releases pointed in the variables.

local.conf example:
QEMU_VERSION=2.1.0
LIBVIRT_VERSION=1.2.7

Change-Id: I89d20609fbfc8791892ab103c7b25c1334e3e94d
Signed-off-by: Michele Paolino <m.paolino@virtualopensystems.com>