Fix CodeNarc warning about empty catch

Change-Id: Id7509ebafe7949879cf661f5b797ee14525a96f2
diff --git a/validate-cloud.groovy b/validate-cloud.groovy
index 5dd8008..788a989 100644
--- a/validate-cloud.groovy
+++ b/validate-cloud.groovy
@@ -76,6 +76,7 @@
                              report_dir = REPORT_DIR
                          }
                     } catch (MissingPropertyException e) {
+                        // No action on MissingPropertyException
                     }
                     def rally_variables = ["floating_network=${FLOATING_NETWORK}",
                                            "rally_image=${RALLY_IMAGE}",