Class NetworkStorageDevice

Create a NetworkStorage Device instance. Note this class is only
to be used as a baseclass and then only with multiple inheritance.
The only correct use is:
class MyStorageDevice(StorageDevice, NetworkStorageDevice):

The sole purpose of this class is to:
1) Be able to check if a StorageDevice is network backed
   (using isinstance).
2) To be able to get the host address of the host (server) backing
   the storage *or* the NIC through which the storage is connected

Arguments:

    host_address -- host address of the backing server
    nic -- nic to which the storage is bound

Overrides: object.__init__