test: stabilize overlayfs candidate assertion #178

Job	Run time
Container E2E Full (private-same-sandbox)	8m 0s
Container E2E Full (host-to-private)	7m 12s
Container E2E Smoke (host-pid-same-sandbox)	1m 50s
Container E2E Full (private-to-child-container)	7m 2s
	24m 4s

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