Fix usage of period configuration value
Fix usage of period configuration value

Configuration of period value was broken with the merging of
"Refactor Orchestrator" patch: using CONF.collect.period at the
module level does not ensure that the value from configuration
file will be used (because the configuration file may not have
been loaded at module import time)

This patch fixes this problem

Change-Id: Id0fb85ee9bb70f7d315ba24b1ffd62b5ee630f2f
Closes-Bug: 1666906

openstack/cloudkitty,stackforge/cloudkitty,stackforge/cloudkitty,openstack/cloudkitty