Add missing per service Keystone config augments

The task for keystone is missing a 'per service' entry for it's config
augments. This means for example that users could not add:

/etc/kolla/config/keystone/keystone-fernet.conf

or

/etc/kolla/config/keystone/keystone.conf

and have keystone.conf augmented for those services only.

Change-Id: I8d2570b4a52dc6c3552397b0a6fa7866133dc2f1
Closes-Bug: #1646898