The tripleo_nova_image_cache role was relying on a future mtime to convince
nova image cleanup logic to skip a specific image that we want to pre-cache.
This works well on nodes that are not currently hosting an instance of the
image, however if there is an instance using it then nova will reset the mtime
every 40 minutes (by default).
As a result it's not possible to provide fine grained control of the caching.
We can just ensure the image exists on the host with an mtime of now.
It should remain cache for at least remove_unused_original_minimum_age_seconds
from nova.conf (default 86400).
Change-Id: If836759020bcaeb0d3af47f2af7f98ff2150b606
(cherry picked from commit 359ef43f94)
(cherry picked from commit 4757aa3500)
1d21542f40