Fix some warning in workflow.groovy

After jenkins update we start to get warning like
"Did you forget the `def` keyword?..field named status_style
(to a value of type String) which could
lead to memory leaks or other issues"
so add def for places we've missed it

Related: PRODX-52357
Change-Id: I4dddd30778d5cd910a9706419e30181c17d34514
diff --git a/src/com/mirantis/mk/Http.groovy b/src/com/mirantis/mk/Http.groovy
index a7e0f97..2a9bd95 100644
--- a/src/com/mirantis/mk/Http.groovy
+++ b/src/com/mirantis/mk/Http.groovy
@@ -154,7 +154,7 @@
     }
 
     if ( connection.responseCode >= 200 && connection.responseCode < 300 ) {
-        res = connection.inputStream.text
+        def res = connection.inputStream.text
         try {
             return new groovy.json.JsonSlurperClassic().parseText(res)
         } catch (Exception e) {