New qdev_init_nofail()

Like qdev_init(), but terminate program via hw_error() instead of
returning an error value.

Use it instead of qdev_init() where terminating the program on failure
is okay, either because it's during machine construction, or because
we know that failure can't happen.

Because relying in the latter is somewhat unclean, and the former is
not always obvious, it would be nice to go back to qdev_init() in the
not-so-obvious cases, only with proper error handling.  I'm leaving
that for another day, because it involves making sure that error
values are properly checked by all callers.

Patchworks-ID: 35168
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
