Auth: Make IOException non retriable

[ajaaym]

Fix #3573 Making IOException non retriable. Since most of Auth implementation based on network are already retrying for common problems and there are more IOException that are not retriable.

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[ajaaym]

I signed it

[ejona86]

NAK. This was done on purpose in #3757 to fix #3267. This is cross-language gRPC behavior. The more common case is simply there was an I/O failure getting the token and retrying will fix it. If the client has no valid token then things are broken anyway; if an application-level retry forever retries, that seems like its own problem.

[ajaaym]

@ejona86 Thanks for the review and background. Reason I thought to put back this change is bcz google-auth-library-java already retries the common cause so when it comes here its normally not-retriable. Closing this and will take up the discussion on google-auth-library-java.

[ejona86]

@ajaaym, hmmm... That was added in googleapis/google-auth-library-java#104 . I wasn't aware of that (I reviewed many of the initial changes in google-auth-library-java and was an old maintainer for google-{http,oauth,api}-java-client). Go ahead and include me in the conversation with google-auth-library-java. It seems the problem is that google-auth-library-java is retrying for 18 minutes, if I'm reading ExponentialBackOff correctly (see DEFAULT_MAX_ELAPSED_TIME_MILLIS and nextBackOffMillis(); 900000 ms is 18 minutes, not 15...).