CLOUDSTACK: ex_list_nics, ex_add_nic_to_vm, ex_remove_nic_from_vm + test...

Functionality to list NICS and to add/remove them too.
And some extra attribute maps with respect to nics.
Including unit tests
Some cosmetic (indent) change slipped in this commit as well.
Maybe better and more consistent names would be attach and detach (attach_nic_to_node, detach_nic_from_node).