Make glance cache management cron task idempotent

Use a seed in the glance cache management cron task's random
filter so that each host's results are idempotent when re-running.
This prevents the constant changing of the crontab whenever the
playbook is run.

Change-Id: Ia14e867347aeadc6c55cef49f9f2ae0e6f86412f

tasks/glance_post_install.yml

@@ -109,7 +109,7 @@
 - name: Create glance cache management cron jobs
   cron:
     name: "{{ item.name }}"
-    minute: "{{ 59 |random(start=1) }}"
+    minute: "{{ 59 | random(seed=inventory_hostname, start=1) }}"
     day: "*"
     hour: "{{ item.hour }}"
     month: "*"