Add a new test target for rollback observer.

The tests were failing the first time on postsubmit because of test from
some other file. All the tests would pass on retry. Creating a new
target for rollback observer because we want them to run reliably.

Test: manual
Bug: 291137901
Change-Id: I7c4730391235bbbc07a98f17518d54037ff905e4
4 files changed