Mark BWC tests as awaits fix

These tests are awaiting the BWC indices script to be upgraded for 5.x.

Original commit: elastic/x-pack-elasticsearch@540fe73bd0

elasticsearch/src/test/java/org/elasticsearch/AbstractOldXPackIndicesBackwardsCompatibilityTestCase.java

@@ -96,6 +96,7 @@ public abstract class AbstractOldXPackIndicesBackwardsCompatibilityTestCase exte
         }
     }
 
+    @AwaitsFix(bugUrl = "https://github.com/elastic/x-plugins/issues/3908")
     public void testAllVersionsTested() throws Exception {
         SortedSet<String> expectedVersions = new TreeSet<>();
         for (Version v : VersionUtils.allVersions()) {
@@ -114,6 +115,7 @@ public abstract class AbstractOldXPackIndicesBackwardsCompatibilityTestCase exte
         }
     }
 
+    @AwaitsFix(bugUrl = "https://github.com/elastic/x-plugins/issues/3908")
     public void testOldIndexes() throws Exception {
         Collections.shuffle(dataFiles, random());
         for (String dataFile : dataFiles) {
@@ -134,6 +136,10 @@ public abstract class AbstractOldXPackIndicesBackwardsCompatibilityTestCase exte
         }
     }
 
+    public void testEmpty() {
+        // empty test so test suite does not fail for no tests
+    }
+
     /**
      * Should we test this version at all? Called before loading the data directory. Return false to skip it entirely.
      */