Change runtest 'overriding test def' log to silent.

Change-Id: I9b52aac04f2b95e9c93963bfad0c6d29dbddb87d

Author: Brett Chabot

testrunner/test_defs/test_defs.py

@@ -96,7 +96,7 @@ def _AddTest(self, test):
       test: TestSuite to add
     """
     if self.GetTest(test.GetName()) is not None:
-      logger.Log("Overriding test definition %s" % test.GetName())
+      logger.SilentLog("Overriding test definition %s" % test.GetName())
     self._testname_map[test.GetName()] = test
 
   def GetTests(self):