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/tools/UpdateSmdCommandTest.java

@@ -73,6 +73,8 @@ public class UpdateSmdCommandTest extends CommandTestCase<UpdateSmdCommand> {
 
   @Before
   public void init() {
+    // Setting the clock used for SignedMark signature validity.
+    TmchCertificateAuthority.clock = () -> DateTime.parse("2015-01-01TZ");
     inject.setStaticField(Ofy.class, "clock", clock);
     createTld("xn--q9jyb4c");
     clock.advanceOneMilli();