cmd/go: run the gpg command verbosely in TestScript/version_buildvcs_git_gpg

cmd/go: run the gpg command verbosely in TestScript/version_buildvcs_git_gpg

Also update test helper programs to avoid the deprecated io/ioutil
package and fix minor formatting issues.

For #49649.

Change-Id: Id404acbb2795470420854d682f849d959d2080c0
Reviewed-on: https://go-review.googlesource.com/c/go/+/453775
Auto-Submit: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>