Add glance-cache-cleaner and glance-cache-pruner

* glance::cache::cleaner: Installs a cron job to remove stalled and
  invalid cached images.
* glance::cache::pruner: Installs a cron job to keep the image cache
  at or below the maximum cache size.

Change-Id: I99cb1809446f1a1126454ff5fa5bdceb8044ee28
Merge "Add glance-cache-cleaner and glance-cache-pruner"