This change introduces a new nova-status check to ensure a machine type
has been recorded for each instance within an environment.
nova-status will fail with a warning when instances are found, directing
the operator to use the previously added nova-manage list_unset and
update commands to set a machine type for these instances. The logic for
this check comes entirely from the list_unset command.
It is noted in the warning output that this can be ignored if no libvirt
or HyperV based computes are present in the environment as
hw_machine_type is only used by these two virt drivers at present.
blueprint: libvirt-default-machine-type
Change-Id: Ic3ae48c57e61c4e45883fbae1328a448be025953
8cddd243bf