This adds implicit rollback support during A/B style updates.
If you explicitly start a checkpoint with -1, needsRollback will
trigger if the update fails, and should be used if any additional
cleanup is needed that is not covered by A/B itself.
Test: All Checkpoint tests pass
Bug: 111020314
Change-Id: I88b4a1098c6bac4dc1438a54c8a8f59577a6c17b
Checkpointing uses a combination of files on the meta partition
and the checkpoint= fs_mgr flag. Checkpointed partitions will
revert to their starting state on reboot unless checkpoint commit
is called.
Test: Run vdc commands, check file on metadata
Merged-In: Icba16578608a6cbf922472e9d4ae5b8cf5f016c6
Change-Id: Icba16578608a6cbf922472e9d4ae5b8cf5f016c6
