Teach exception_detector.rb to deal with escaped tabs (\u0009) …

[mbert]

This PR fixes parts of #33: Tabs in Java stacktraces are dealt with correctly. The unit test has been extended accordingly.

Missing:

• Python and Ruby (of which I don't know enough to start modifying regular expressions)
• Other escaped characters if that plays a role at all (depends on what stack traces in other languages may look like)

With this patch applied collecting Java stacktraces from a log stream in a Kubernetes cluster works for me. Without it does not.

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[mbert]

I signed the CLA.

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[DandyDeveloper]

@qingling128 Can we get someone to review this? It's got some easy to fix conflicts.

It's been open a very long time.

[igorpeshansky]

Sorry, this fell through the cracks.

This plugin is designed to work with Stackdriver Error Reporting, which should recognize the resulting multiline message as a stack trace. I'm verifying this with the team right now, but I suspect that it won't recognize those Unicode escapes, even if the stack trace were joined into a single log entry.

These Unicode escapes are unexpected, and should have been decoded by the JSON parser before they ever get to this plugin. If you have a simple repro case for producing such escapes in a Java stack trace, let's debug that (in #33) and ensure that this plugin sees the original tab instead.

[igorpeshansky]

For the record, a self-service way to verify how Error Reporting will handle your message is to pipe it into the following command:

gcloud beta error-reporting events report \
  --service manual \
  --service-version test-version \
  --project=$(gcloud config get-value project) \
  --message-file=/dev/stdin

and check the results on the Error Reporting page in the Cloud Console.

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