For example, can use `goroutine all bt` to dump all goroutines'
information.

Change-Id: I51b547c2b837913e4bdabf0f45b28f09250a3e34
GitHub-Last-Rev: d04dcd4f581f97e35ee45969a864f1270d79e49b
GitHub-Pull-Request: golang/go#26283
Reviewed-on: https://go-review.googlesource.com/c/go/+/122589
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: David Chase <drchase@google.com>