testing: expose Chatty flag

[alberts]

Please provide any additional information below.

After Go 1.

https://groups.google.com/forum/?fromgroups#!topic/golang-dev/-g7k7Hes4ZA

The idea is to allow tests that run like this:

go test -c foo && sudo ./foo.test

or in any other way where the go tool isn't running it, and which has third-party
logging code, to give an indication that the test could disable that logging.

[ality]

Comment 1:

Labels changed: added priority-later, removed priority-triage.

[minux]

Comment 2:

This issue was closed by revision 20bf1a9.

Status changed to Fixed.