Revert "Revert "Add a qa/rolling-upgrade test that does single-document index and deletes""

This reverts commit elastic/x-pack@94b65dcf52.

Original commit: elastic/x-pack-elasticsearch@abd90463f8

qa/rolling-upgrade/src/test/resources/rest-api-spec/test/mixed_cluster/10_basic.yaml

@@ -30,6 +30,27 @@
           - '{"index": {"_index": "test_index", "_type": "test_type"}}'
           - '{"f1": "v5_mixed", "f2": 9}'
 
+ - do:
+     index:
+       index: test_index
+       type: test_type
+       id: d10
+       body: {"f1": "v6_mixed", "f2": 10}
+
+ - do:
+     index:
+       index: test_index
+       type: test_type
+       id: d11
+       body: {"f1": "v7_mixed", "f2": 11}
+
+ - do:
+     index:
+       index: test_index
+       type: test_type
+       id: d12
+       body: {"f1": "v8_mixed", "f2": 12}
+
  - do:
      indices.flush:
         index: test_index
@@ -38,4 +59,22 @@
      search:
         index: test_index
 
- - match: { hits.total: 10 } # 5 docs from old cluster, 5 docs from mixed cluster
+ - match: { hits.total: 13 } # 5 docs from old cluster, 8 docs from mixed cluster
+
+ - do:
+     delete:
+       index: test_index
+       type: test_type
+       id: d10
+
+ - do:
+     delete:
+       index: test_index
+       type: test_type
+       id: d11
+
+ - do:
+     delete:
+       index: test_index
+       type: test_type
+       id: d12