Fix multistring global variables output for Workflow

Related-to: PRODX-29788

Change-Id: Ia30835cd7e628ac97ef2425b7e889b4f79e50e4a
diff --git a/src/com/mirantis/mk/Workflow.groovy b/src/com/mirantis/mk/Workflow.groovy
index 29e7b83..e4d75bf 100644
--- a/src/com/mirantis/mk/Workflow.groovy
+++ b/src/com/mirantis/mk/Workflow.groovy
@@ -28,7 +28,7 @@
 def printVariables(global_variables) {
     def message = "// Collected global_variables during the workflow:\n"
     for (variable in global_variables) {
-        message += "env.${variable.key}=\"${variable.value}\"\n"
+        message += "env.${variable.key}=\"\"\"${variable.value}\"\"\"\n"
     }
     common.warningMsg(message)
 }