Unity: add hlu property to lun.host_access

[Murray-LIANG]

Currently, the user needs to work around it using:

In [30]: host = lun.host_access[0].host                                                                                                                                                       

In [31]: host                                                                                                                                                                                 
Out[31]: 
{
    "UnityHost": {
        "existed": true,
        "hash": 8745316769505,
        "id": "Host_13",
        "name": "10.226.198.144"
    }
}

In [32]: host.update()
… snip …

In [33]: host.host_luns                                                                                                                                                                       
Out[33]: 
{
    "UnityHostLunList": [
        {
            "UnityHostLun": {
                "existed": true,
                "hash": 8745316615176,
                "hlu": 0,
                "id": "Host_13_sv_17001_prod",
                "lun": {
                    "UnityLun": {
                        "hash": 8745316615218
                    }
                }
            }
        }
    ]
}

In [34]: host.host_luns[0].hlu                                                                                                                                                                
Out[34]: 0