cmd/coordinator: tell browsers not to sniff content of log messages

Chrome and other browsers like to suppress output while they sniff the
content; tell them not to so we see the logs immediately.

Fixes golang/go#10097

Change-Id: I73295a46ff803c1e3f8a092afb225caaa28198bb
Reviewed-on: https://go-review.googlesource.com/7440
Reviewed-by: Andrew Gerrand <adg@golang.org>
1 file changed