Fix Unexpected crash_sender stdout/stderr when testing Official image

logging_KernelCrashServer and logging_UserCrash tests fail on an Official
image, because crash_sender's is_official() test leaks the "Official" line:
grep needs the quiet option (and does not need a cut).

BUG=837
TEST=logging_UserCrash

Signed-off-by: Hugh Dickins <hughd@chromium.org>

Review URL: http://codereview.chromium.org/3357010
diff --git a/crash_reporter/crash_sender b/crash_reporter/crash_sender
index d265e18..37c3362 100644
--- a/crash_reporter/crash_sender
+++ b/crash_reporter/crash_sender
@@ -94,8 +94,7 @@
 }
 
 is_official() {
-  grep ^CHROMEOS_RELEASE_DESCRIPTION /etc/lsb-release | cut -d = -f 2- | \
-      grep Official
+  grep ^CHROMEOS_RELEASE_DESCRIPTION /etc/lsb-release | grep -q Official
 }
 
 # Generate a uniform random number in 0..max-1.