virt: Improve DHCP RFC compatibility

Client can suggest IP address which he wants to have.
Autotest check if IP address is accessible, thanks to
it there is no problem with changing of guest network.
Additionally it helps with windows DHCP compatibility.

Signed-off-by: Jiří Župka <jzupka@redhat.com>
env_process: Fix location where to find qemu_img if it was built

If qemu is built from source, qemu-img will be
located on a symlink

qemu/qemu-img

pointing to the appropriate binary. However, we were
pointing out to the class that creates qemu images
the data dir

shared/data

So the code was trying to find the symlink there,
something that would never ever happen. So let's
point out the right place where qemu-img can be
found, and create the images.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>