[Test] Rolling Upgrade should preserve templates (elastic/x-pack-elasticsearch#1687)

Real upgrades will have preserved their templates, so rolling upgrade tests should preserve them as well and internal services should be expected to replace them as needed.

Original commit: elastic/x-pack-elasticsearch@93a155951e

qa/rolling-upgrade/src/test/java/org/elasticsearch/upgrades/UpgradeClusterClientYamlTestSuiteIT.java

@@ -67,6 +67,11 @@ public class UpgradeClusterClientYamlTestSuiteIT extends SecurityClusterClientYa
         return true;
     }
 
+    @Override
+    protected boolean preserveTemplatesUponCompletion() {
+        return true;
+    }
+
     public UpgradeClusterClientYamlTestSuiteIT(ClientYamlTestCandidate testCandidate) {
         super(testCandidate);
     }