KCM: Implement an internal ccache storage and retrieval API In order for the KCM server to work with ccaches stored in different locations, implement a middle-man between the KCM server and the ccache storage. This module has asynchronous API because we can't assume anything about where the ccaches are stored. Reviewed-by: Michal Židek <mzidek@redhat.com> Reviewed-by: Simo Sorce <simo@redhat.com>