code: def create_cgroup(self, name):
          
          node = Node(name, parent=self)
          if node in self.children:
              raise RuntimeError('Node {} already exists under {}'.format(name, self.path))
  
          name = name.encode()
          fp = os.path.join(self.full_path, name)
          os.mkdir(fp)
          self.children.append(node)
          return node
docs: Create a cgroup by name and attach it under this node.