Enable network tags in Haskell code

Prior to the creation of the 2.10 branch, network tags were broken, and
the Haskell code introduced there mistakenly accepted this as the
desired functionality. This patch fixes this in a very simple way.
Signed-off-by: Hrvoje Ribicic <riba@google.com>
Reviewed-by: Klaus Aehlig <aehlig@google.com>

src/Ganeti/Query/Server.hs

@@ -158,12 +158,10 @@ handleCall cdata QueryClusterInfo =
 handleCall cfg (QueryTags kind name) = do
   let tags = case kind of
                TagKindCluster  -> Ok . clusterTags $ configCluster cfg
-               TagKindGroup    -> groupTags <$> Config.getGroup    cfg name
-               TagKindNode     -> nodeTags  <$> Config.getNode     cfg name
-               TagKindInstance -> instTags  <$> Config.getInstance cfg name
-               TagKindNetwork  -> Bad $ OpPrereqError
-                                        "Network tag is not allowed"
-                                        ECodeInval
+               TagKindGroup    -> groupTags   <$> Config.getGroup    cfg name
+               TagKindNode     -> nodeTags    <$> Config.getNode     cfg name
+               TagKindInstance -> instTags    <$> Config.getInstance cfg name
+               TagKindNetwork  -> networkTags <$> Config.getNetwork  cfg name
   return (J.showJSON <$> tags)
 
 handleCall cfg (Query qkind qfields qfilter) = do