machine.list fails for some group_key values

[Huw Wilkins]

When providing group_key to a machine.list call it returns errors for some keys. I only tested a few, but got these errors:

power_state:
"tuple indices must be integers or slices, not str"

owner:
"Cannot resolve keyword 'name' into field. Choices are: consumers, date_joined, email ..."

According the API these are valid keys, as providing in incorrect key results in the error:
Cannot resolve keyword 'nothing' into field. Choices are: address_ttl, agent_name, architecture, bios_boot_method, bmc, bmc_id...