Node capacity locking

If node capacity locking is enabled via the yfs.nodecapacity.lock property, the following sequence takes place:

1. Each capacity check determines whether capacity is below a threshold specified with the yfs.nodecapacity.threshold property.
2. If node capacity is above the threshold, locking is not performed for the desired resource pool and date. If node capacity is below the threshold, then future availability checks will require locking before checking availability. This notifies all other threads for this resource pool and date that a lock is required.
3. Subsequent availability checks will await the lock for the timeout interval specified in the yfs.nodecapacity.timeout property.
4. If this interval expires, the availability check assumes that there is no capacity available and reverts to whatever sourcing and inventory logic is already configured.

Note that the timeout interval can also be configured to wait indefinitely.