Fix ApexManager#snapshotCeData (3/n)

Now it returns a boolean to indicate if the snapshot was successful or
not since we no longer use inode to delete snapshots.

Bug: 154897348
Test: atest RollbackUnitTest RollbackStoreTest AppDataRollbackHelperTest
Change-Id: I10ed0e3adef88a27ee239c183d99a836b623d0d1