Add CUSTOM_KITCHEN_ENVS parameter to salt-formula tests

Change-Id: I36065144607df65c343013afaf6506d86de67116
diff --git a/jenkins/client/job/salt-formulas/tests.yml b/jenkins/client/job/salt-formulas/tests.yml
index 15eff13..c25cc49 100644
--- a/jenkins/client/job/salt-formulas/tests.yml
+++ b/jenkins/client/job/salt-formulas/tests.yml
@@ -158,3 +158,5 @@
               KITCHEN_TESTS_PARALLEL:
                 type: boolean
                 default: 'false'
+              CUSTOM_KITCHEN_ENVS:
+                type: text