use proper mixed version check

Author: davidkyle

x-pack/plugin/transform/src/main/java/org/elasticsearch/xpack/transform/action/TransportUpgradeTransformsAction.java

@@ -29,7 +29,6 @@
 import org.elasticsearch.threadpool.ThreadPool;
 import org.elasticsearch.transport.TransportService;
 import org.elasticsearch.xpack.core.XPackSettings;
-import org.elasticsearch.xpack.core.ml.utils.TransportVersionUtils;
 import org.elasticsearch.xpack.core.security.SecurityContext;
 import org.elasticsearch.xpack.core.transform.TransformMetadata;
 import org.elasticsearch.xpack.core.transform.action.UpgradeTransformsAction;
@@ -107,7 +106,7 @@ protected void masterOperation(Task ignoredTask, Request request, ClusterState s
         }
 
         // do not allow in mixed clusters
-        if (TransportVersionUtils.isMinTransportVersionSameAsCurrent(state) == false) {
+        if (state.nodes().isMixedVersionCluster()) {
             listener.onFailure(
                 new ElasticsearchStatusException("Cannot upgrade transforms while cluster upgrade is in progress.", RestStatus.CONFLICT)
             );

x-pack/qa/rolling-upgrade/src/test/java/org/elasticsearch/upgrades/TransformSurvivesUpgradeIT.java

@@ -239,7 +239,7 @@ private void verifyUpgradeFailsIfMixedCluster() {
         final Request upgradeTransformRequest = new Request("POST", getTransformEndpoint() + "_upgrade");
 
         Exception ex = expectThrows(Exception.class, () -> client().performRequest(upgradeTransformRequest));
-        assertThat(ex.getMessage(), containsString("All nodes must be the same version"));
+        assertThat(ex.getMessage(), containsString("Cannot upgrade transforms while cluster upgrade is in progress"));
     }
 
     private void verifyUpgrade() throws IOException {