Support for "usage" for "Cloud" nodes. Fixes https://github.com/GNS3/gns3-gui/issues/2887

Allow "usage" for all builtin nodes (not exposed in Ui).

gns3server/compute/dynamips/nodes/device.py

@@ -31,6 +31,7 @@ class Device:
     def __init__(self, name, node_id, project, manager, hypervisor=None):
 
         self._name = name
+        self._usage = ""
         self._id = node_id
         self._project = project
         self._manager = manager
@@ -76,6 +77,26 @@ class Device:
 
         self._name = new_name
 
+    @property
+    def usage(self):
+        """
+        Returns the usage for this device.
+
+        :returns: usage
+        """
+
+        return self._usage
+
+    @usage.setter
+    def usage(self, new_usage):
+        """
+        Sets the usage of this device.
+
+        :param new_usage: usage
+        """
+
+        self._usage = new_usage
+
     @property
     def id(self):
         """