Add test for rollback of same version apk.

The test is marked @Ignore because of a bug in RollbackManager that
fails to expire a rollback when there is a new update of an apk to its
same version code:

STACKTRACE:
java.lang.AssertionError: expected null, but was:<android.content.rollback.RollbackInfo@28c0495>
  at org.junit.Assert.fail(Assert.java:88)
  at org.junit.Assert.failNotNull(Assert.java:755)
  at org.junit.Assert.assertNull(Assert.java:737)
  at org.junit.Assert.assertNull(Assert.java:747)
  at com.android.tests.rollback.RollbackTestUtils.getUniqueRollbackInfoForPackage(RollbackTestUtils.java:321)
  at com.android.tests.rollback.RollbackTest.testSameVersionUpdate(RollbackTest.java:795)

Bug: 120200473
Test: atest RollbackTest
Change-Id: Ib03692c170ee689fcf667689dad25647e55f984f