Fix flaky testEnableRollbackTimeoutFailsRollback test

We no longer block on the handler thread in getAvailableRollbacks. That
means it is possible we see an available rollback left over from a
previous test run. Update the test to ensure previous rollbacks are
removed and give sufficient time to make a new rollback available before
concluding that no rollback will be made available in this case.

Test: atest RollbackTest:com.android.tests.rollback.RollbackTest#testEnableRollbackTimeoutFailsRollback
Change-Id: Id94d5452836b07d6f802758bd0dfdd3c276a3c05

tests/RollbackTest/RollbackTest/src/com/android/tests/rollback/RollbackTest.java

@@ -1020,6 +1020,7 @@ public class RollbackTest {
 
             Uninstall.packages(TestApp.A);
             Install.single(TestApp.A1).commit();
+            waitForUnavailableRollback(TestApp.A);
 
             // Block the RollbackManager to make extra sure it will not be
             // able to enable the rollback in time.
@@ -1028,6 +1029,10 @@ public class RollbackTest {
 
             assertThat(InstallUtils.getInstalledVersion(TestApp.A)).isEqualTo(2);
 
+            // Give plenty of time for RollbackManager to unblock and attempt
+            // to make the rollback available before asserting that the
+            // rollback was not made available.
+            Thread.sleep(TimeUnit.SECONDS.toMillis(2));
             assertThat(
                 getUniqueRollbackInfoForPackage(rm.getAvailableRollbacks(), TestApp.A)).isNull();
         } finally {