Check whether Rabbitmq user's permissions need to be changed.

def _check_perms_changes(name, newperms, runas=None, existing=None):
    '''
    Check whether Rabbitmq user's permissions need to be changed.
    '''
    if not newperms:
        return False

    if existing is None:
        try:
            existing = __salt__['rabbitmq.list_user_permissions'](name, runas=runas)
        except CommandExecutionError as err:
            log.error('Error: %s', err)
            return False

    perm_need_change = False
    for vhost_perms in newperms:
        for vhost, perms in six.iteritems(vhost_perms):
            if vhost in existing:
                existing_vhost = existing[vhost]
                if perms != existing_vhost:
                    # This checks for setting permissions to nothing in the state,
                    # when previous state runs have already set permissions to
                    # nothing. We don't want to report a change in this case.
                    if existing_vhost == '' and perms == ['', '', '']:
                        continue
                    perm_need_change = True
            else:
                perm_need_change = True

    return perm_need_change