If a VM is already loaded, we return a VM instead of creating it twice

Partial fix for #81

gns3server/modules/base_manager.py

@@ -200,6 +200,9 @@ class BaseManager:
         :param vm_id: restore a VM identifier
         """
 
+        if vm_id in self._vms:
+            return self._vms[vm_id]
+
         project = ProjectManager.instance().get_project(project_id)
         if vm_id and isinstance(vm_id, int):
             with (yield from BaseManager._convert_lock):

tests/modules/test_manager.py

@@ -34,6 +34,20 @@ def test_create_vm_new_topology(loop, project, port_manager):
     assert vm in project.vms
 
 
+def test_create_twice_same_vm_new_topology(loop, project, port_manager):
+
+    project._vms = set()
+    VPCS._instance = None
+    vpcs = VPCS.instance()
+    vpcs.port_manager = port_manager
+    vm_id = str(uuid.uuid4())
+    vm = loop.run_until_complete(vpcs.create_vm("PC 1", project.id, vm_id, console=2222))
+    assert vm in project.vms
+    assert len(project.vms) == 1
+    vm = loop.run_until_complete(vpcs.create_vm("PC 2", project.id, vm_id, console=2222))
+    assert len(project.vms) == 1
+
+
 def test_create_vm_new_topology_without_uuid(loop, project, port_manager):
 
     VPCS._instance = None