Return true if the alias is set

    CLI Example:

    .. code-block:: bash

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

def has_pair(ip, alias):
    '''
    Return true if the alias is set

    CLI Example:

    .. code-block:: bash

        salt '*' hosts.has_pair <ip> <alias>
    '''
    hosts = _list_hosts()
    try:
        return alias in hosts[ip]
    except KeyError:
        return False