Keycloak user and groups for api commands are always keycloak

[Guiiix]

Hi,

It seems that keycloak_user and keycloak_group resource params are never used when calling kcadm. The reason of that is keycloak_user ||= 'keycloak' and keycloak_group ||= 'keycloak' always set both variables to keycloak even if @keycloak_user and @keycloak_group are defined.

With this fix, values set through keycloak_api resource are used, otherwise default values are set.

BTW, thank you for your work, this module is a masterpiece.