Add tests for DE_sys and CE apex data rollback.

This adds tests in StagedRollbackTest for apex data directory rollback.

The test performs the following steps:

- Push files into the apex data directory
- Update the APEX with rollback enabled
- Remove files from data directory
- Add new files to data directory
- Roll back the update
- Verify old files are restored

Bug: 141148175
Test: atest StagedRollbackTest#testRollbackApexDataDirectories_DeSys
Test: atest StagedRollbackTest#testRollbackApexDataDirectories_Ce
Change-Id: Ie1e7ed626c0b654c19b23bfcb008ac4d717aafe2