http2: Fix issue where slow requests are terminated prematurely

[hyperair]

This PR fixes an issue where http2 requests taking longer than 500ms will be terminated prematurely, with http2.request silently resolving with truncated responses instead of rejecting with an error.

The issue comes from starting the idle shutdown timer (500ms) immediately after the beginning of the latest request on the session, and not detecting that the session is still actively transferring data before forcefully terminating the session.

This PR fixes that by switching the connection idle shutdown timer to session.setTimeout instead of setTimeout.

I've also verified that this fix makes the client in https://github.com/hyperair/google-http2-bug-demo work correctly (more info here):

• all requests return the correct untruncated data
• client process shuts down properly after all requests are done

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Fixes #768 🦕

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[sofisl]

/gcbrun

[sofisl]

Actually, could we add a test to specifically make sure test errors are not swallowed prematurely (per your issue description)? TY!

[sofisl]

So sorry, I'm going to close this for now since we are in the middle of migrating this repo to google-cloud-node. would you mind reopening this PR on that repo when the migration is finished (probably next week) and just add a test as described above? TYSM!

[hyperair]

Sure, could you drop me a ping on this issue when the migration's done please?