'Get cgroup\'s name
:param: pwd: cgroup name
:return: cgroup\'s name'

def get_cgroup_name(self, pwd=None):

    if (pwd is None):
        return None
    if isinstance(pwd, int):
        pwd = self.cgroups[pwd]
    if pwd.startswith((self.root + '/')):
        return pwd[(len(self.root) + 1):]
    return None
