Bug 1040708 - Use the preset workloads defined in b2gpopulate

Added WORKLOADS to b2gpopulate/__init__.py so that the preset
values of the WORKLOADS can be used in other tools.
Merge pull request #26 from gakiwate/BUG_1040708

Bug 1040708 - Expose the preset workloads. r=dhunt
Bug 1040708 - Bump version to 0.27. r=me