autotest: lower logging rate

we are starting to get huge downloads for autotest failures. High
logging rates rarely help to diagnose an issue, so lower the default
rate when in autotest

Tools/autotest/vehicle_test_suite.py

@@ -3254,6 +3254,9 @@ def customise_SITL_commandline(self,
     def default_parameter_list(self):
         ret = {
             'LOG_DISARMED': 1,
+            # also lower logging rate to reduce log sizes
+            'LOG_DARM_RATEMAX': 5,
+            'LOG_FILE_RATEMAX': 10,
         }
         if self.force_ahrs_type is not None:
             if self.force_ahrs_type == 2: