QemuOpts: Drop qemu_opts_foreach() parameter abort_on_failure

When the argument is non-zero, qemu_opts_foreach() stops on callback
returning non-zero, and returns that value.

When the argument is zero, it doesn't stop, and returns the bit-wise
inclusive or of all the return values.  Funky :)

The callers that pass zero could just as well pass one, because their
callbacks can't return anything but zero:

* qemu_add_globals()'s callback qdev_add_one_global()

* qemu_config_write()'s callback config_write_opts()

* main()'s callbacks default_driver_check(), drive_enable_snapshot(),
  vnc_init_func()

Drop the parameter, and always stop.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Acked-by: Kevin Wolf <kwolf@redhat.com>

net/vhost-user.c

@@ -245,7 +245,7 @@ int net_init_vhost_user(const NetClientOptions *opts, const char *name,
 
     /* verify net frontend */
     if (qemu_opts_foreach(qemu_find_opts("device"), net_vhost_check_net,
-                          (char *)name, true) == -1) {
+                          (char *)name)) {
         return -1;
     }