cmd/vet: eliminate use of Perl in tests

cmd/vet: eliminate use of Perl in tests

This change uses errorCheck and wantedErrors functions copied from
the test/run.go to eliminate use of the test/errchk perl script.

Tests' error messages that contained full filenames were changed to
have base filenames because the errorCheck function processes output
from "go vet" in the same way.

Fixes #20032.

Change-Id: Ieb7be67c2d7281b9648171c698398449b7e2d4dd
Reviewed-on: https://go-review.googlesource.com/114176
Run-TryBot: Yury Smolsky <yury@smolsky.by>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>