R1:62360ea40689

Adjust the Drydock allocator to limit each pending lease to one allocating resource

Summary:
Ref T13677. Currently, one lease may cause multiple resources to allocate simultaneously if it starts allocating one, then wakes up from a yield later on and still sees no available resources.

This is never desired -- or, at least, produces desirable behavior only entirely by accident. Normally, it causes an excess of resources to allocate.

This is not a catastrophic problem: the extra resources usually get used…