The TestParseErrors test function was not strict with unwanted errors
received from url.Parse(). It was not failing in such cases, now it does.

Change-Id: I18a26a68c1136f5c762989a76e04b47e33dd35f1
GitHub-Last-Rev: c33f9842f7908f27012859e25caa79388cc2785a
GitHub-Pull-Request: golang/go#32954
Reviewed-on: https://go-review.googlesource.com/c/go/+/185080Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>