Introduce Task Info Table

- move 'input', 'message' and 'result' columns to table 'task_info'
- introduce migration script for the above db changes.
- appropriate tests are included

Co-authored-by: Nikhil Komawar <nikhil.komawar@rackspace.com>

partly implements bp async-glance-workers

Change-Id: I9867d609f4729572b72a44d1f05e353acf6c98d9