Fix build breakage after exclusive storage commits

This fixes:

htest/Test/Ganeti/Rpc.hs:50:14:
    Couldn't match expected type `Rpc.RpcCallNodeInfo'
           against inferred type `Data.Map.Map String Bool
                                  -> Rpc.RpcCallNodeInfo'
    In the first argument of `(<$>)', namely `Rpc.RpcCallNodeInfo'
    In the first argument of `(<*>)', namely
        `Rpc.RpcCallNodeInfo <$> arbitrary'

by adding the new parameter (empty map for now), and also:

ganeti/constants.py:432:5: E123 closing bracket does not match
   indentation of opening bracket's line

By switching to 2-char indentation and (for consistency) also replaces
frozenset(…) with our unique checker (UniqueFrozenset).

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Bernardo Dal Seno <bdalseno@google.com>