Raise error if using a non linked clone VM twice

Fix https://github.com/GNS3/gns3-gui/issues/1593

tests/compute/dynamips/test_dynamips_manager.py

@@ -28,7 +28,7 @@ from gns3server.compute.dynamips.dynamips_error import DynamipsError
 from unittest.mock import patch
 
 
-@pytest.fixture(scope="module")
+@pytest.fixture
 def manager(port_manager):
     m = Dynamips.instance()
     m.port_manager = port_manager

tests/compute/dynamips/test_dynamips_router.py

@@ -26,7 +26,7 @@ from gns3server.compute.dynamips import Dynamips
 from gns3server.config import Config
 
 
-@pytest.fixture(scope="module")
+@pytest.fixture
 def manager(port_manager):
     m = Dynamips.instance()
     m.port_manager = port_manager