Don't allow user to overwrite GNS3 docker environment variables

Fix #1098

gns3server/compute/docker/docker_vm.py

@@ -313,7 +313,10 @@ class DockerVM(BaseNode):
         params["Env"].append("GNS3_VOLUMES={}".format(":".join(self._volumes)))
 
         if self._environment:
-            params["Env"] += [e.strip() for e in self._environment.split("\n")]
+            for e in self._environment.split("\n"):
+                e = e.strip()
+                if not e.startswith("GNS3_"):
+                    params["Env"].append(e)
 
         if self._console_type == "vnc":
             yield from self._start_vnc()

tests/compute/docker/test_docker_vm.py

@@ -30,8 +30,7 @@ from gns3server.compute.docker import Docker
 from gns3server.utils.get_resource import get_resource
 
 
-from unittest.mock import patch, MagicMock, PropertyMock, call
-from gns3server.config import Config
+from unittest.mock import patch, MagicMock, call
 
 
 @pytest.fixture()
@@ -244,15 +243,19 @@ def test_create_start_cmd(loop, project, manager):
 
 
 def test_create_environment(loop, project, manager):
+    """
+    Allow user to pass an environnement. User can't override our
+    internal variables
+    """
 
     response = {
         "Id": "e90e34656806",
         "Warnings": []
     }
-    with asyncio_patch("gns3server.compute.docker.Docker.list_images", return_value=[{"image": "ubuntu"}]) as mock_list_images:
+    with asyncio_patch("gns3server.compute.docker.Docker.list_images", return_value=[{"image": "ubuntu"}]):
         with asyncio_patch("gns3server.compute.docker.Docker.query", return_value=response) as mock:
             vm = DockerVM("test", str(uuid.uuid4()), project, manager, "ubuntu")
-            vm.environment = "YES=1\nNO=0"
+            vm.environment = "YES=1\nNO=0\nGNS3_MAX_ETHERNET=eth2"
             loop.run_until_complete(asyncio.async(vm.create()))
             mock.assert_called_with("POST", "containers/create", data={
                 "Tty": True,