Try loading all policy files even if some files are invalid
Try loading all policy files even if some files are invalid

This change ensures that horizon tries to load all policy files even
if an invalid policy file is found, so that horizon can use as many
policy rules as it can parse.

Closes-Bug: #1917483
Change-Id: I24f8da71460129ee7162af5f307a7e405addb15d

ChameleonCloud/horizon,openstack/horizon,ChameleonCloud/horizon,openstack/horizon,ChameleonCloud/horizon,openstack/horizon,ChameleonCloud/horizon,openstack/horizon