virt-host-validate: Initialize the error object

virt-host-validate: Initialize the error object

Several libvirt functions are called from virt-host-validate.
Some of these functions do report an error on failure. But
reporting an error is coupled with freeing previous error (by
calling virResetError()). But we've never called
virErrorInitialize() and thus resetting error object frees some
random pointer.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Fabiano Fidêncio <fabiano@fidencio.org>