Make a logging statement more contextual. (#704)

diff --git a/mobly/base_test.py b/mobly/base_test.py
index c9b9fab..9d30e60 100644
--- a/mobly/base_test.py
+++ b/mobly/base_test.py
@@ -605,7 +605,9 @@
         except signals.TestAbortSignal:
           raise
         except Exception as e:
-          logging.exception(e)
+          logging.exception('Exception occurred in %s of %s.',
+                            STAGE_NAME_TEARDOWN_TEST,
+                            self.current_test_info.name)
           tr_record.test_error()
           tr_record.add_error(STAGE_NAME_TEARDOWN_TEST, e)
           teardown_test_failed = True