As described in the design doc about storage types,
we plan to generalize the RPC call "node info" wrt to
storage types. This patch extends the call by accepting
a list of storage units, that is not only identified
by storage type and identifier, but enhanced by additional
parameters. So far, only LVM storage has an additional
parameter, which is the 'exclusive storage' flag. This
patch enhances the backend code of the node info call
to be able to handle this change.

Signed-off-by: Helga Velroyen <helgav@google.com>
Reviewed-by: Thomas Thrainer <thomasth@google.com>