qemu_opt_set() is a wrapper around qemu_opt_set() that reports the
error with qerror_report_err().
Most of its users assume the function can't fail. Make them use
qemu_opt_set_err() with &error_abort, so that should the assumption
ever break, it'll break noisily.
Just two users remain, in util/qemu-config.c. Switch them to
qemu_opt_set_err() as well, then rename qemu_opt_set_err() to
qemu_opt_set().
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>