Opentracing Spec incompability: `error` tag not setting span to be failed

[jizhang27]

From standard span tags on opentracing spec, error tag should be respected to "decide if and only if the application considers the operation represented by the Span to have failed" true if and only if the application considers the operation represented by the Span to have failed.

Currently we are relying on those three tags instead: ['error.type', 'error.msg', 'error.stack'].
reference

Hope that I can get some feedback. Will be happy to make a PR for it if necessary, thanks.

[rochdev]

@jizhang27 Thanks for the suggestion! I think it does indeed make sense to support this.

Basically the error field would simply have to be changed to 1 when the error tag is true. I would probably discard the tag itself in the formatter since the backend uses the field and not the tag to classify errors.

Please let me know if you will make a PR to avoid duplicating the work.

[jizhang27]

@rochdev Thanks for the quick response. PR is created please take a look!