Possibly fix flaky ChangeIT#rebase test

Get the change from the server to assert the current revision instead
of retrieving this information from the index. It may be that stale
index data is the reason for this test being flaky.

Change-Id: Ieff5e3f5dc44702baa7114bb62c88866e324641d
Signed-off-by: Edwin Kempin <ekempin@google.com>

gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/api/change/ChangeIT.java

@@ -238,7 +238,8 @@ public class ChangeIT extends AbstractDaemonTest {
         .rebase();
 
     // Second change should have 2 patch sets
-    assertThat(r2.getPatchSetId().get()).isEqualTo(2);
+    ChangeInfo c2 = gApi.changes().id(r2.getChangeId()).get();
+    assertThat(c2.revisions.get(c2.currentRevision)._number).isEqualTo(2);
 
     // ...and the committer should be correct
     ChangeInfo info = gApi.changes()