Fix missing err short assignment in Go Metrics

[bluk]

It seems that err is not declared properly for some of the code snippets. It seems that it was removed in #484 .

Some of the other changes also seemed unnecessary for some functions (like naming the error return value (terr error) but not using terr). One change that may want to be investigated further is:

https://github.com/census-instrumentation/opencensus-website/pull/484/files#diff-4d73bb710d0b193312291ce07a0b156cL620

where the log.Fatal(err) replaces return err. The log.Fatal will cause a panic and I believe does not work correctly with the intended behavior in line 686 ( https://github.com/census-instrumentation/opencensus-website/pull/484/files#diff-4d73bb710d0b193312291ce07a0b156cL686 ) where any returned error is checked to be io.EOF and normally returns.

[odeke-em]

Thank you for the fix @bluk! LGTM /cc @hvent90

[odeke-em]

Some of the other changes also seemed unnecessary for some functions (like naming the error return value (terr error) but not using terr).

@bluk (terr error) is used when capturing metrics at the end of the function, it was named because we want to capture the ending error regardless of the statement, in the cases were (err error) would be taken

[bluk]

Ahh right. I was looking at the earlier snippets where terr isn't used yet, but in the final end-to-end program, it is used. Cool.