[dev.fuzz] testing, internal/fuzz: multiple small fixes

[dev.fuzz] testing, internal/fuzz: multiple small fixes

* Run gofmt with go1.17 build constraint changes.
* Tighten regular expressions used in tests. "ok" got some false
  positives with verbose output, so make sure it appears at the start
  of a line.
* Return err in deps.RunFuzzWorker instead of nil.
* Call common.Helper from F methods. This prevents F methods from
  appearing in stack traces.

Change-Id: I839c70ec8a9f313c1a4ea68e6bb34a4d801dd36f
Reviewed-on: https://go-review.googlesource.com/c/go/+/297032
Trust: Jay Conrod <jayconrod@google.com>
Trust: Katie Hockman <katie@golang.org>
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>