_get_host_device param incorrect for s390x

[jichenjc]

https://github.com/openstack/os-brick/commit/641337bec28adddae742a86faf592e360afdd1d8#diff-fc0623f8e70d3f7227e540c84c0546c5L78

made some changes but now we have _get_host_devices for s390x and x86

https://github.com/openstack/os-brick/blob/master/os_brick/initiator/connectors/fibre_channel_s390x.py#L49

https://github.com/openstack/os-brick/blob/master/os_brick/initiator/connectors/fibre_channel.py#L271

so we need adjust s390x and (power) as well.