Global Expiry progress updates

As an administrator of a large instance I would like to have regular status updates regarding the progress of the global expiry process. Especially when modifying the scope of the Global Expiry the process can run for hours or days with no indication of it's current progress.

To assist administrators in understanding the impacts in their environments we should add a regular log message to the atlassian-bamboo.log file similar to:

"Build Expiry: X% completed" or "Deployment Expiry: Y% Completed".