Merge branch '6.x' into ccr-6.x

* 6.x:
  Avoid randomization bug in FeatureAwareTests

server/src/test/java/org/elasticsearch/cluster/FeatureAwareTests.java

@@ -107,7 +107,7 @@ public Optional<String> getRequiredFeature() {
     }
 
     public void testVersion() {
-        final Version version = VersionUtils.randomVersion(random());
+        final Version version = randomValueOtherThan(VersionUtils.getFirstVersion(), () -> VersionUtils.randomVersion(random()));
         for (final Custom custom : Arrays.asList(new NoRequiredFeatureCustom(version), new RequiredFeatureCustom(version))) {
             {
                 final BytesStreamOutput out = new BytesStreamOutput();