Change waitForProcessing to use exponential backoff #3796

Job	Run time
Upload debug artifacts (nightly-latest)	4m 52s
Upload debug artifacts (linked)	5m 55s
Upload debug artifacts (stable-v2.20.3)	6m 10s
Upload debug artifacts (default)	6m 0s
Download and check debug artifacts	9s
	23m 6s

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