log the location of the detailed log file

The idea is that if someone reads the short log and scratches her head, she can
notice that there is a more detailed log available.

Change-Id: Id5f443f1af0dc774d4d4c588a238b786a83e44d3

src/osmo_gsm_tester/trial.py

@@ -65,14 +65,16 @@ class Trial(log.Origin):
     def __enter__(self):
         # add a log target to log to the run dir
         run_dir = self.get_run_dir()
+        detailed_log = run_dir.new_child(FILE_LOG)
         self.log_targets = [
-            log.FileLogTarget(run_dir.new_child(FILE_LOG))
+            log.FileLogTarget(detailed_log)
               .set_all_levels(log.L_DBG)
               .style_change(trace=True),
             log.FileLogTarget(run_dir.new_child(FILE_LOG_BRIEF))
               .style_change(src=False, all_origins=False)
             ]
         self.log('Trial start')
+        self.log('Detailed log at', detailed_log)
         self.take()
         super().__enter__()