Add rollback data policy (1/n)

1. Do the plumbing to pass the data policy all the way to
   SessionInfo.
2. SessionInfo#rollbackDataPolicy will be used by RollbackManager to
   determine whether to wipe user data when enabling/committing
   rollback.

Bug: 144683152
Test: atest RollbackStoreTest RollbackUnitTest AppDataRollbackHelperTest
Test: atest RollbackTest StagedRollbackTest

Change-Id: Ie1e5457d0304f9cf8fc34fce17d707be75407a2b