Clean up rollbacks and test apps

See comment#6.

Clean up rollbacks and test apps before and after running tests.
This ensure we are in a good and expected condition when running tests.

Bug: 154080003
Test: atest RollbackTest
Test: atest MultiUserRollbackTest
Test: atest NetworkStagedRollbackTest
Test: atest StagedRollbackTest

Change-Id: If10fc8865e644611f1cf6a9db9d6dca6c7f11aee