Fix trouble with builtin devices when we free ports

Fix #825

gns3server/compute/dynamips/nodes/frame_relay_switch.py

@@ -119,24 +119,31 @@ class FrameRelaySwitch(Device):
         self._mappings = mappings
 
     @asyncio.coroutine
-    def delete(self):
-        """
-        Deletes this Frame Relay switch.
-        """
-
+    def close(self):
         for nio in self._nios.values():
             if nio and isinstance(nio, NIOUDP):
                 self.manager.port_manager.release_udp_port(nio.lport, self._project)
 
-        try:
-            yield from self._hypervisor.send('frsw delete "{}"'.format(self._name))
-            log.info('Frame Relay switch "{name}" [{id}] has been deleted'.format(name=self._name, id=self._id))
-        except DynamipsError:
-            log.debug("Could not properly delete Frame relay switch {}".format(self._name))
+        if self._hypervisor:
+            try:
+                yield from self._hypervisor.send('frsw delete "{}"'.format(self._name))
+                log.info('Frame Relay switch "{name}" [{id}] has been deleted'.format(name=self._name, id=self._id))
+            except DynamipsError:
+                log.debug("Could not properly delete Frame relay switch {}".format(self._name))
+
         if self._hypervisor and self in self._hypervisor.devices:
             self._hypervisor.devices.remove(self)
         if self._hypervisor and not self._hypervisor.devices:
             yield from self.hypervisor.stop()
+            self._hypervisor = None
+
+    @asyncio.coroutine
+    def delete(self):
+        """
+        Deletes this Frame Relay switch.
+        """
+        yield from self.close()
+        return True
 
     def has_port(self, port):
         """