Replace JSONDecodeError by ValueError (Python 3.4 compatibility)

Fix #847

gns3server/controller/__init__.py

@@ -127,7 +127,7 @@ class Controller:
                 self.save()
             with open(self._config_file) as f:
                 data = json.load(f)
-        except (OSError, json.decoder.JSONDecodeError) as e:
+        except (OSError, ValueError) as e:
             log.critical("Cannot load %s: %s", self._config_file, str(e))
             return
 

gns3server/controller/gns3vm/virtualbox_gns3_vm.py

@@ -234,7 +234,7 @@ class VirtualBoxGNS3VM(BaseGNS3VM):
             if resp:
                 try:
                     json_data = yield from resp.json()
-                except json.decoder.JSONDecodeError:
+                except ValueError:
                     pass
                 resp.close()
 

gns3server/controller/topology.py

@@ -112,7 +112,7 @@ def load_topology(path):
     try:
         with open(path, encoding="utf-8") as f:
             topo = json.load(f)
-    except (OSError, UnicodeDecodeError, json.decoder.JSONDecodeError) as e:
+    except (OSError, UnicodeDecodeError, ValueError) as e:
         raise aiohttp.web.HTTPConflict(text="Could not load topology {}: {}".format(path, str(e)))
     if "revision" not in topo or topo["revision"] < 5:
         # If it's an old GNS3 file we need to convert it