Add an utility function for triples

Ganeti/HTools/Utils.hs

@@ -25,6 +25,7 @@ module Ganeti.HTools.Utils
     (
       debug
     , sepSplit
+    , fst3
     , varianceCoeff
     , commaJoin
     , readEitherString
@@ -72,6 +73,10 @@ sepSplit sep s
 commaSplit :: String -> [String]
 commaSplit = sepSplit ','
 
+-- | Simple version of 'fst' for a triple
+fst3 :: (a, b, c) -> a
+fst3 (a, _, _) = a
+
 -- * Mathematical functions
 
 -- Simple and slow statistical functions, please replace with better versions