R1:9b29d46e60f3

Make Drydock lease infrastructure more nimble

Summary:
Ref T9252. Currently, Harbormaster does this when trying to acquire a working copy:

- Ask for a working copy.
- Yield for 15 seconds.
- Check if we have a working copy yet.

That's OK, but Drydock takes ~1s to acquire a working copy lease if a resource is already available, so we end up doing this:

- T+0: Ask for a working copy.
- T+0: Yield for 15 seconds.
- T+1: Working copy lease activates.
- T+15: Working copy lease is used.