Update shrink's bwc version to 6.1.0 and enabled bwc tests

build.gradle

@@ -186,7 +186,7 @@ task verifyVersions {
  * after the backport of the backcompat code is complete.
  */
 allprojects {
-  ext.bwc_tests_enabled = false
+  ext.bwc_tests_enabled = true
 }
 
 task verifyBwcTestsEnabled {

core/src/main/java/org/elasticsearch/action/admin/indices/shrink/ResizeAction.java

@@ -27,7 +27,7 @@ public class ResizeAction extends Action<ResizeRequest, ResizeResponse, ResizeRe
 
     public static final ResizeAction INSTANCE = new ResizeAction();
     public static final String NAME = "indices:admin/resize";
-    public static final Version COMPATIBILITY_VERSION = Version.V_7_0_0_alpha1; // TODO remove this once it's backported
+    public static final Version COMPATIBILITY_VERSION = Version.V_6_1_0; // TODO remove this once it's backported
 
     private ResizeAction() {
         super(NAME);

core/src/test/java/org/elasticsearch/cluster/routing/allocation/ResizeAllocationDeciderTests.java

@@ -19,6 +19,7 @@
 package org.elasticsearch.cluster.routing.allocation;
 
 import org.elasticsearch.Version;
+import org.elasticsearch.action.admin.indices.shrink.ResizeAction;
 import org.elasticsearch.cluster.ClusterName;
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.ESAllocationTestCase;
@@ -245,7 +246,7 @@ public class ResizeAllocationDeciderTests extends ESAllocationTestCase {
 
     public void testAllocateOnOldNode() {
         Version version = VersionUtils.randomVersionBetween(random(), Version.V_5_0_0,
-            VersionUtils.getPreviousVersion(Version.V_7_0_0_alpha1));
+            VersionUtils.getPreviousVersion(ResizeAction.COMPATIBILITY_VERSION));
         ClusterState clusterState = createInitialClusterState(true, version);
         MetaData.Builder metaBuilder = MetaData.builder(clusterState.metaData());
         metaBuilder.put(IndexMetaData.builder("target").settings(settings(Version.CURRENT)

rest-api-spec/src/main/resources/rest-api-spec/test/indices.split/10_basic.yml

@@ -1,8 +1,8 @@
 ---
 "Split index via API":
   - skip:
-      version: " - 6.99.99"
-      reason: Added in 7.0.0
+      version: " - 6.0.99"
+      reason: Added in 6.1.0
   - do:
       indices.create:
         index: source

rest-api-spec/src/main/resources/rest-api-spec/test/indices.split/20_source_mapping.yml

@@ -1,8 +1,8 @@
 ---
 "Split index ignores target template mapping":
   - skip:
-      version: " - 6.99.99"
-      reason: added in 7.0.0
+      version: " - 6.0.99"
+      reason: Added in 6.1.0
 
   # create index
   - do: