bug #1075018 and bug #1078594 are very serious issues with the image
cache manager when using shared storage. We couldn't address the
issues in time for 2012.2.1 because of the riskiness of the changes
required.
As a workaround, disable that code by default using:
image_cache_manager_interval=0
Change-Id: Iab78abf855e919bc3d3278a39882ff6d39bd3c1c