[chores] Added more descriptive log warnings

openwisp_monitoring/check/classes/iperf.py

@@ -23,14 +23,16 @@ def check(self, store=True):
         device = self.related_object
         device_connection = self._get_device_connection(device)
         if not device_connection:
-            logger.warning(f'{device}: connection not properly set, Iperf skipped!')
+            logger.warning(
+                f'"DeviceConnection is not properly set for "{device}", iperf check skipped!'
+            )
             return
         device_connection.connect()
-        # We need to check device_connection is_working just right after connect().
-        # because it may be possible that authentication (publickey) failed.
-        # or any other failure happened during connect().
-        if not device_connection.is_working:
-            logger.warning(f'{device}: SSH connection is not working, Iperf skipped!')
+        # The DeviceConnection could fail if the management tunnel is down.
+        if not device_connection.connect():
+            logger.warning(
+                f'Failed to get a working DeviceConnection for "{device}", iperf check skipped!'
+            )
             return
         servers = self._get_iperf_servers(device.organization.id)
         command = f'iperf3 -c {servers[0]} -J'