Fix 'List' instance of 'PyValue'

Fix 'List' instance of 'PyValue' to properly convert Haskell lists to
Python lists.
Signed-off-by: Jose A. Lopes <jabolopes@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>

src/Ganeti/PyValueInstances.hs

@@ -52,7 +52,7 @@ instance PyValue String where
   showValue = show
 
 instance PyValue a => PyValue [a] where
-  showValue xs = show (map showValue xs)
+  showValue xs = "[" ++ intercalate "," (map showValue xs) ++ "]"
 
 instance (PyValue k, PyValue a) => PyValue (Map k a) where
   showValue mp =