Add missing "Filters" section to the ironic-images.filters

The ironic-images.filters file is missing the [Filters] section. This
will cause the ironic-rootwrap command to fail.

Change-Id: I3780fc89e0144093a40035e6b91fcf946bbdf6a3
Partial-Bug: #1268674
Merge "Add missing "Filters" section to the ironic-images.filters"