client: skip shutdown delay when tasks already deregistered

[mismithhisler]

Description

When all the tasks in an allocation have completed, the allocation will run the PostRun hooks, and deregister the task. When that happens, it is not necessary to wait on the shutdown_delay during garbage collection.

Testing & Reproduction steps

Links

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[tgross]

LGTM! It'd be nice if we can expand any test cases that cover this behavior.

[mismithhisler]

LGTM! It'd be nice if we can expand any test cases that cover this behavior.

Since this looks like the right direction, I will look into adding some test cases for it.

[jrasell]

LGTM with a few minor comments inline.