Do cleanup before/after running the test

Somehow rollbacks related to testappA are not cleaned before running the
test and cause test failures. See b/150653097#comment2 for more details.

Let's clean rollbacks manually to have a clean start.

Bug: 150653097
Test: atest MultiUserRollbackTest
Change-Id: I4eb126e193f76c821d26fc62115263b86066a215