Reduce the image cache manager periodic interval.
Reduce the image cache manager periodic interval.

When this code was written, I (incorrectly) believed a periodic
task tick was about a second. It turns out that by default they're
between 60 seconds and 120 seconds depending on a random value.
Therefore, reduce the interval to something more reasonable.

Change-Id: Id840c755f954e3e371d7238243f2248e8d402c7b

yrobla/nova,sileht/deb-openstack-nova,eneabio/nova,yrobla/nova,eneabio/nova,sileht/deb-openstack-nova,yrobla/nova,sileht/deb-openstack-nova,eneabio/nova