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/controller/project.py

@@ -875,7 +875,7 @@ class Project:
                 link = yield from self.add_link(link_id=link_data["link_id"])
                 if "filters" in link_data:
                     yield from link.update_filters(link_data["filters"])
-                for node_link in link_data["nodes"]:
+                for node_link in link_data.get("nodes", []):
                     node = self.get_node(node_link["node_id"])
                     port = node.get_port(node_link["adapter_number"], node_link["port_number"])
                     if port is None:
@@ -903,7 +903,7 @@ class Project:
             try:
                 if os.path.exists(path + ".backup"):
                     shutil.copy(path + ".backup", path)
-            except (PermissionError, OSError):
+            except OSError:
                 pass
             self._status = "closed"
             self._loading = False
@@ -968,7 +968,7 @@ class Project:
                 with open(project_path, "rb") as f:
                     project = yield from import_project(self._controller, str(uuid.uuid4()), f, location=location, name=name, keep_compute_id=True)
         except (ValueError, OSError, UnicodeEncodeError) as e:
-            raise aiohttp.web.HTTPConflict(text="Can not duplicate project: {}".format(str(e)))
+            raise aiohttp.web.HTTPConflict(text="Cannot duplicate project: {}".format(str(e)))
 
         if previous_status == "closed":
             yield from self.close()