Add a host to an existing entry, if the entry is not in place then create
    it with the given host

    CLI Example:

    .. code-block:: bash

        salt '*' hosts.add_host <ip> <alias>

def add_host(ip, alias):
    '''
    Add a host to an existing entry, if the entry is not in place then create
    it with the given host

    CLI Example:

    .. code-block:: bash

        salt '*' hosts.add_host <ip> <alias>
    '''
    hfn = _get_or_create_hostfile()
    if not os.path.isfile(hfn):
        return False

    if has_pair(ip, alias):
        return True

    hosts = _list_hosts()

    # Make sure future calls to _list_hosts() will re-read the file
    __context__.pop('hosts._list_hosts', None)

    inserted = False
    for i, h in six.iteritems(hosts):
        for j in range(len(h)):
            if h[j].startswith('#') and i == ip:
                h.insert(j, alias)
                inserted = True
    if not inserted:
        hosts.setdefault(ip, []).append(alias)
    _write_hosts(hosts)
    return True