log/syslog: fix channel race in test.
log/syslog: fix channel race in test.

R=golang-dev, minux.ma, iant, bradfitz, dave
CC=golang-dev
https://codereview.appspot.com/7314057

Committer: Dave Cheney <bfcdf3e6ca6cef45543bfbb57509c92aec9a39fb@cheney.net>
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go