Another attempt to deflake TestPullFromCentralRegistryImplicitRefParts

Retries after v1 fallbacks were added in #20411. The test still appears
to be flaky. There are two potential problems. The initial pull was not
protected against pulling from v1, so it could be giving us a different
hello-world image to compare against. Also, after experiencing a v1
fallback, we need to restore the original image before doing the next
pull, because otherwise the "Image is up to date for hello-world:latest"
message will not show up as expected.

See #17214.

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>