Fix a flaky test

It is possible to have multiple committed rollbacks which include the
same app.

Uninstalling an app will delete committed rollbacks which include
the app. However, there is a race condition between when the app is
uninstalled and when rollback manager deletes the rollback as is stated
here:

https://cs.corp.google.com/android/frameworks/base/tests/RollbackTest/RollbackTest/src/com/android/tests/rollback/RollbackTest.java?rcl=75dfeca3d40624b745f41155aa38bc5e3fa405fe&l=116

We hit the assertion in #getUniqueRollbackInfoForPackage when there are
multiple rollbacks including the same package which is caused by the
race condition above.

Let's rewrite the code by calling #hasRollbackInclude instead which will
not throw.

Also do some cleanup in the xml to improve the isolation of our tests.

Bug: 152271716
Test: atest RollbackTest
Change-Id: Iad3effe52db2a0d2d5e3914bcd08ed93926f3fd3