Hardware subtypes should permit multiple values

[glennmatthews]

OVFs can specify multiple subtypes for a device (allowing the target host to choose which subtype it prefers/supports):

        <rasd:ResourceSubType>virtio E1000</rasd:ResourceSubType>

but cot edit-hardware doesn't presently provide this option:

$ cot edit-hardware foo.ova --nic-type e1000 virtio
cot: error: unrecognized arguments: virtio
$ cot edit-hardware foo.ova --nic-type "e1000 virtio"
cot edit-hardware: error: argument --nic-type: invalid choice: 'e1000 virtio' (choose from 'e1000', 'virtio', 'vmxnet3')
$ cot edit-hardware foo.ova --nic-type "e1000, virtio"
cot edit-hardware: error: argument --nic-type: invalid choice: 'e1000, virtio' (choose from 'e1000', 'virtio', 'vmxnet3')
$ cot edit-hardware foo.ova --nic-type e1000 --nic-type virtio
# accepted as valid but the resulting OVA only has virtio subtype

[glennmatthews]

Fixed in v1.5.0