fix: resume iterator on EOS internal error

[larkee]

Fixes#120

This fixes the same issue as googleapis/java-spanner#360.

A similar issue was encountered by bigquery-storage and was fixed in googleapis/google-cloud-python#9994.

[hengfengli]

I think we need to add retry for "Received unexpected EOS on DATA frame from server" error message as well.

[thiagotnunes]

@larkee thanks for the fix, I will test it out with a long running PDML to make sure everything we need is in place!

[tseaver]

This change really needs unit test coverage: I'm not sure why the Kokoro build is passing without it.

[thiagotnunes]

@larkee Quick update, the PDML long running task finished successfully in production testing. Thanks for fixing this!

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The unit test coverage is back to 100% for all files touched by this change.

[hengfengli]

LGTM. 👍