[CVP,master] Fix DEBUG_MODE for cvp-tempest

Related-PROD: PROD-31355

Change-Id: Iada733c53d7d17b74869e22e1285b2843b6d09f2
diff --git a/cvp-tempest.groovy b/cvp-tempest.groovy
index c311186..d7c508d 100644
--- a/cvp-tempest.groovy
+++ b/cvp-tempest.groovy
@@ -171,7 +171,7 @@
             junit "${report_prefix}.xml"
         }
     } finally {
-        if (DEBUG_MODE == 'false') {
+        if ( ! DEBUG_MODE.toBoolean() ) {
             validate.runCleanup(saltMaster, TARGET_NODE, container_name)
         }
     }