Code review comment for ~ltrager/maas:s390x-power-driver

Thanks for the review. I've added support for detecting if zhmcclient is missing from the system and gracefully ignoring it.

My node-uuid branch[1] adds support to MAAS to detect the hardware_uuid in lshw output during commissioning and allows booting using the hardware_uuid as an identifier. A user can't edit this value it must be discovered during commissioning. On S390X the hardware_uuid is used to identify which LPAR to power control and is the only way to identify a system while booting. Because MAAS needs to be able to identify the system node_field allows the user defined hardware_uuid from the power driver to be automatically copied to the node model. This allows us to avoid having to do an extra database query into the BMC model when systems are booting.

I did this generically using the name node_field as I could see this being useful for other power drivers in the future. For example virsh hosts normally use the same name for the VM ID and hostname.

[1] https://code.launchpad.net/~ltrager/maas/+git/maas/+merge/360110