fix(ksonnet-util): default variable name secretName (#312)

Author: Duologic

ksonnet-util/kausal.libsonnet

@@ -45,11 +45,9 @@ k {
           + super.fromConfigMap(name, configMapName, configMapItems),
 
         // Shortcut constructor for secret volumes.
-        fromSecret(name, secret='', secretName='')::
-          if secretName != ''
-          then local secret = secretName;
-               super.withName(name) +
-               super.mixin.secret.withSecretName(secret),
+        fromSecret(name, secretName)::
+          super.withName(name) +
+          super.mixin.secret.withSecretName(secretName),
 
         // Rename emptyDir to claimName
         fromPersistentVolumeClaim(name='', claimName=''):: super.fromPersistentVolumeClaim(name=name, emptyDir=claimName),