Run the glance cache cron jobs more frequently

Currently, running every 24 hours is long enough to allow the cache to
completely fill up the container's disk. By running the jobs every 6
hours instead (4 times per day), we hope to eliminate the problem where
the container will fill up.

Closes-bug: 1439892
Change-Id: Ie7311f70656447382c2403e79453fe88401efca1

playbooks/roles/os_glance/tasks/glance_post_install.yml

@@ -16,7 +16,7 @@
 - name: Create glance cache management cron jobs
   cron:
     name: "{{ item.name }}"
-    minute: "{{ 59 |random }}"
+    minute: "{{ 59 |random(start=1) }}"
     day: "*"
     hour: "{{ item.hour }}"
     month: "*"
@@ -27,7 +27,7 @@
     - name: /usr/local/bin/glance-cache-pruner
       hour: "*"
     - name: /usr/local/bin/glance-cache-cleaner
-      hour: "{{ 23|random }}"
+      hour: "*/5"
   when: glance_flavor | search("cache")
   tags:
     - glance-cron