Merge branch '2.1' into 2.2

# Conflicts:
#	gns3server/compute/builtin/nodes/cloud.py
#	gns3server/compute/docker/docker_vm.py
#	gns3server/compute/dynamips/nodes/ethernet_switch.py
#	gns3server/compute/iou/iou_vm.py
#	gns3server/compute/qemu/qemu_vm.py
#	gns3server/compute/virtualbox/virtualbox_vm.py
#	gns3server/compute/vmware/vmware_vm.py
#	gns3server/controller/__init__.py
#	gns3server/version.py
#	gns3server/web/web_server.py

gns3server/compute/dynamips/nodes/ethernet_switch.py

@@ -87,6 +87,7 @@ class EthernetSwitch(Device):
         self._mappings = {}
         self._telnet_console = None
         self._telnet_shell = None
+        self._telnet_server = None
         self._console = console
         self._console_type = console_type
 
@@ -233,8 +234,9 @@ class EthernetSwitch(Device):
         """
 
         yield from self._telnet.close()
-        self._telnet_server.close()
-        
+        if self._telnet_server:
+            self._telnet_server.close()
+
         for nio in self._nios.values():
             if nio:
                 yield from nio.close()