Define TestRule that manages cache use in tests

All current tests that use caches with custom data expiry values
now restore the default config when teardown. We need to prevent
new unsafe uses from being introduced.

Restoration code have also been added to a few other tests that modifies
static fields.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=228888041

javatests/google/registry/tools/server/RefreshDnsForAllDomainsActionTest.java

@@ -14,6 +14,7 @@
 
 package google.registry.tools.server;
 
+import static com.google.common.truth.Truth.assertThat;
 import static google.registry.testing.DatastoreHelper.createTld;
 import static google.registry.testing.DatastoreHelper.createTlds;
 import static google.registry.testing.DatastoreHelper.persistActiveDomain;
@@ -30,6 +31,7 @@ import google.registry.testing.InjectRule;
 import google.registry.testing.mapreduce.MapreduceTestCase;
 import google.registry.tools.server.RefreshDnsForAllDomainsAction.RefreshDnsForAllDomainsActionMapper;
 import org.joda.time.DateTime;
+import org.junit.After;
 import org.junit.Before;
 import org.junit.Rule;
 import org.junit.Test;
@@ -44,16 +46,23 @@ public class RefreshDnsForAllDomainsActionTest
   @Rule public final InjectRule inject = new InjectRule();
 
   private final DnsQueue dnsQueue = mock(DnsQueue.class);
+  private DnsQueue origDnsQueue;
 
   @Before
   public void init() {
-    inject.setStaticField(RefreshDnsForAllDomainsActionMapper.class, "dnsQueue", dnsQueue);
+    origDnsQueue = RefreshDnsForAllDomainsActionMapper.setDnsQueueForTest(dnsQueue);
 
     action = new RefreshDnsForAllDomainsAction();
     action.mrRunner = makeDefaultRunner();
     action.response = new FakeResponse();
   }
 
+  @After
+  public void restoreDnsQueue() {
+    assertThat(RefreshDnsForAllDomainsActionMapper.setDnsQueueForTest(origDnsQueue))
+        .isEqualTo(dnsQueue);
+  }
+
   private void runMapreduce() throws Exception {
     action.run();
     executeTasksUntilEmpty("mapreduce");