Avoid abort in case of projects with no helm charts customization, e.g. voltha-system-tests

inserting --set for bbsim to avoid helm error

Change-Id: I4cf24af2b49bc63db094b703efb066e7353af412
diff --git a/jjb/pipeline/voltha/master/bbsim-tests.groovy b/jjb/pipeline/voltha/master/bbsim-tests.groovy
index 5b15e10..7332054 100644
--- a/jjb/pipeline/voltha/master/bbsim-tests.groovy
+++ b/jjb/pipeline/voltha/master/bbsim-tests.groovy
@@ -52,10 +52,9 @@
     break
     case "bbsim":
       // BBSIM has a different format that voltha, return directly
-      return "images.bbsim.tag=citest,images.bbsim.pullPolicy=Never"
+      return "--set images.bbsim.tag=citest,images.bbsim.pullPolicy=Never"
     break
     default:
-      throw new Exception("Don't know how to customize helm flags for custom image on project ${project}")
     break
   }