net_scale: Don't instantiate NetInfo needlessly

network validation used to instantiate full-blown NetInfo objects
when it just needed bondings() and nics(). This patch fixes that
by calling only for the information that it needs.

Bug-Url: https://bugzilla.redhat.com/1053114
Change-Id: I729c522396095a8114fefbc600dab00b46cea2bb
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/23576
Reviewed-by: Dan Kenigsberg <danken@redhat.com>