Be more atomic when counting nodes

When supplying the allocator with information on supply and demand,
count the nodes starting from one query result.  Otherwise, we might
end up miscounting when a node transitions state.

This has perhaps a negligible impact in production, but a noticable
impact on tests.  Either way, it was wrong.

Change-Id: I2ceaf61d6a55ac1d20243ad8d032a87f4daca07e
Merge "Be more atomic when counting nodes"