Improve LUQueryNodes for lockless case

In most uses of LUQueryNodes, we don't take a lock. This means that the
instance data is not protected across GetInstanceList and
GetInstanceInfo, and this can lead to instances not existing anymore.

Switching to GetAllInstanceInfo means that we get a single,
semi-consistent snapshot (since instances can still be modified, but
it's much better).

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>