testing: fix -run behavior with fuzz tests

This change fixes some issues with -run, and
the subsequent command line output when running
in verbose mode. It replaces CorpusEntry.Name
with CorpusEntry.Path, and refactors the code
accordingly.

This change also adds a lot of additional tests
which check explicit command line output when
fuzz targets are run without fuzzing. This will
be important to avoid regressions.

Updates #48149

Change-Id: If34b1f51db646317b7b51c3c38ae53231d01f568
Reviewed-on: https://go-review.googlesource.com/c/go/+/354632


Trust: Katie Hockman <katie@golang.org>
Run-TryBot: Katie Hockman <katie@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>