Move keystone logs over to oslofrmt

After the successful implementation of
https://blueprints.launchpad.net/keystone/+spec/unified-logging-in-keystone
keystone uses oslo logging instead of its own. Update logstash settings
to reflect this.

We currently don't have any keystone logs in logstash, this should fix
that.

Change-Id: I7acfa35bfd112a15d2ec3aa7338fb28b37a827cb
Merge "Move keystone logs over to oslofrmt"