Increase interface detach polling period
Increase interface detach polling period

The gate has started failing due to interface detaches timing out.
Examining the logs, it looks like Nova's interface detach retry takes about
6s to run one attempt. Heat, on the other hand, does 10 retries at 0.5s
intervals. So if Nova has to retry then Heat will fail.

Increase Heat's polling interval to make it more likely that if Nova
succeeds, Heat will see it.

Change-Id: Ie74980a3f806b8c17e4e494ae979725b0078f135
Closes-Bug: #1585858

openstack/heat,noironetworks/heat,noironetworks/heat,openstack/heat