unittest_runner: Disable logging from unittest.

BUG=none
TEST=make test; and make sure no logging output

Change-Id: I9f38d1b0fee8fbb54ca3f7c118f801be017bd3ad
diff --git a/unittest_runner.py b/unittest_runner.py
index 181e3b3..ba98c83 100755
--- a/unittest_runner.py
+++ b/unittest_runner.py
@@ -4,6 +4,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import logging
 import os
 import sys
 import tempfile
@@ -26,6 +27,7 @@
 
 
 def main(argv):
+  logging.disable(logging.CRITICAL)  # Ignore all logging output from unittest.
   temp_dir = tempfile.mkdtemp()
   total_tests = 0
   passed_tests = 0