Fix the import for filter_utils
Fix the import for filter_utils

Changed from importing utils and calling it via utils.filter_utils
to a proper import utils.__init__.py didn't export it so the way it
was called probably worked for python 2 only.

This way is a more ubiquitous way of calling it.

Change-Id: Ie6a073dc286f0d8704c67f8295dfd76bce7897bb

openstack/mistral,openstack/mistral