After a Drydock lease triggers a resource to be reclaimed, stop it from triggering another reclaim until the first one completes

Summary:
Depends on D19752. Ref T13210. If resources take a long time to reclaim/destroy (normally, more than 15 seconds) a single new lease may update several times during the reclaim/destroy process and end up reclaiming multiple resources.

Instead: after a lease triggers a reclaim, prevent it from triggering another reclaim as long as the resource it is reclaiming hasn't finished its reclaim/destroy cycle. Basically, each lease only gets to destroy one resource at a time.

Test Plan:

• Added a sleep(120) to destroyResource() to simulate a long reclaim/destroy cycle.
• Allocated A, A, A working copies. Leased a B working copy.
• Before patch: saw "B" lease destroy all three "A" working copies after ~0, ~15, and ~30 seconds, then build a new "B" resource after ~120 seconds (when the first reclaim/destroy finished).
• After patch: saw "B" lease destroy one "A" working copy after ~0 seconds, then wait patiently until it finished up, then build a new "B" resource.

Reviewers: amckinley

Reviewed By: amckinley

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T13210

Differential Revision: https://secure.phabricator.com/D19753