Enable node filtering to filter nodes not created.
Enable node filtering to filter nodes not created.

In some condition, the created_at of a node will be None,
filter_bad_nodes() does not filter these kind of nodes.

Closes-Bug: #1614450

Change-Id: Iee3d97659c0d9fd235b016addf820de32b7e1c75

stackforge/senlin,openstack/senlin,openstack/senlin,openstack/senlin,stackforge/senlin