Improve warning message in template rendering (#5806)

* improve warning message when template is none

* improve error message when template is none

* improve error message when template is none

* improve error message when template is none

homeassistant/components/binary_sensor/template.py

@@ -118,7 +118,8 @@ class BinarySensorTemplate(BinarySensorDevice):
             if ex.args and ex.args[0].startswith(
                     "UndefinedError: 'None' has no attribute"):
                 # Common during HA startup - so just a warning
-                _LOGGER.warning(ex)
+                _LOGGER.warning('Could not render template %s,'
+                                ' the state is unknown.', self._name)
                 return
-            _LOGGER.error(ex)
+            _LOGGER.error('Could not render template %s: %s', self._name, ex)
             self._state = False