Factorize `init-keycloak` of addons

The addons have each a specific init-keycloak script that does the same things:

1. define some variables to connect to keycloak
2. get the admin token
3. create a client

This could be factorized by:

1. include keycloak-vars.j2
2. include keycloak-create-client.j2

This must be done after #232 (closed)