Trilio-Configurator charm should pull keystone data from keystone relation

[asbalderson]

The confurator charm should be able to link to keystone to pull in the following required configuration fields:
tv-keystone-admin-url
tv-keystone-public-url
tv-os-username
tv-os-password
tv-os-tenant-name
tv-os-region-name
tv-os-domain-id
tv-os-trustee-role
See the charm layer here: https://github.com/openstack/charm-interface-keystone-admin