Gather group members

def _gather_group_members(group, groups, users):
    '''
    Gather group members
    '''
    _group = __salt__['group.info'](group)

    if not _group:
        log.warning('Group %s does not exist, ignoring.', group)
        return

    for member in _group['members']:
        if member not in users:
            users[member] = groups[group]