read old version of data and use multiple connections to db

cts tests are in Change-Id: Ifcc89b4ff484c7c810fd2d450ded212a43360dda
dependency on: Change-Id: I938c42afc3fb50f5296d01c55ffcf4a102d8b0cb

1. Use sqlite's work-in-progress writeahead logging feature to read old
     versions of data and thus increase concurrency of readers
     even when there is a writer on the database
2. New API executeQueriesInParallel() sets up a database connecion pool
     automatically created and managed by sqlite java layer
3. To increase reader concurrency, add an option to do BEGIN IMMEDIATE xaction
     instead of BEGIN EXCLUSIVE

Change-Id: I3ce55a8a7cba538f01f731736e7de8ae1e2a8a1f