Merge branch '2.2' into 3.0

# Conflicts:
#	gns3server/appliances/Simulator.gns3a
#	gns3server/compute/docker/__init__.py
#	gns3server/compute/docker/docker_vm.py
#	gns3server/version.py

gns3server/compute/docker/__init__.py

@@ -110,7 +110,7 @@ class Docker(BaseManager):
         body = await response.read()
         response.close()
         if body and len(body):
-            if response.headers["CONTENT-TYPE"] == "application/json":
+            if response.headers.get('CONTENT-TYPE') == 'application/json':
                 body = json.loads(body.decode("utf-8"))
             else:
                 body = body.decode("utf-8")