A secret can be stored in a file. It is written at runtime in the
configuration file.
Note it is also possible to write them in the nix store for dev
purposes.
This commit introduces a nixos module for the Openstack Keystone
service. It also provides a optional bootstrap step that creates some
basic initial resources (tenants, endpoints,...).
The provided test starts Keystone by enabling bootstrapping and checks
if user creation works well.
This commit is based on initial works made by domenkozar.
