homing_heaters: Turn off heaters during homing/probing (#2486)

Signed-off-by: Mike Stiemke <fandjango@gmx.de>

klippy/heater.py

@@ -250,6 +250,8 @@ class PrinterHeaters:
         self.register_sensor(config, heater, gcode_id)
         self.available_heaters.append(config.get_name())
         return heater
+    def get_all_heaters(self):
+        return self.available_heaters
     def lookup_heater(self, heater_name):
         if heater_name not in self.heaters:
             raise self.printer.config_error(