Even if use.gcs is false, store block files less then 50,000 bytes in
the Datastore

Change-Id: Ib406cbb571ae170cc3fa3b28ee7a87cdc1fc78a0
Turn use.gcs off by default.

Change-Id: I9c126260e6b9544e7d7d515574c6300dd913240c
Make unit tests work.

Change-Id: I9a48226ed6c091bc5b9a1af40fe5f75122be23fd