hvsupport: Adapt to vbox driver rewrite

hvsupport: Adapt to vbox driver rewrite

Since vbox driver rewrite the virDriver structure init moved from
vbox_tmpl.c into vbox_common.c. However, our hvsupport.pl script
doesn't count with that. It still parses vbox_tmp.c and looks for
virDriver structure which is not found there anymore. As a result,
at hvsupport page is seems like vbox driver doesn't support
anything.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>