Add support for checkpointing

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
Change-Id: Icba16578608a6cbf922472e9d4ae5b8cf5f016c6
9 files changed