feat(cmd/flatten): Add encryption-key-file flag. (#1560)
feat(cmd/flatten): Add encryption-key-file flag. (#1560)

Add an --encryption-key-file flag to the badger flatten tool to support encrypted databases.

Changes:

* Add --encryption-key-file flag
* Set block and index cache sizes to fix panic when running flatten.
dgraph-io/badger,dgraph-io/badger