Set clock used to validate Tmch signature in tests

The signature has expired on Mon Jun 25 23:59:59 UTC 2018.

Instead of fixing all the test files with a new signed mark, we inject the
clock used to validate the signature.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=202116721

javatests/google/registry/flows/domain/DomainCreateFlowTest.java

@@ -151,6 +151,7 @@ import google.registry.model.reporting.DomainTransactionRecord.TransactionReport
 import google.registry.model.reporting.HistoryEntry;
 import google.registry.monitoring.whitebox.EppMetric;
 import google.registry.testing.TaskQueueHelper.TaskMatcher;
+import google.registry.tmch.TmchCertificateAuthority;
 import java.util.Map;
 import org.joda.money.CurrencyUnit;
 import org.joda.money.Money;
@@ -172,6 +173,8 @@ public class DomainCreateFlowTest extends ResourceFlowTestCase<DomainCreateFlow,
 
   @Before
   public void initCreateTest() {
+    // Setting the clock used for SignedMark signature validity.
+    TmchCertificateAuthority.clock = () -> DateTime.parse("2015-01-01TZ");
     createTld("tld");
     persistResource(
         Registry.get("tld")