The keystone_user is deprecated and the os_user module is added since
v2.0.0-0.4.beta2[0], which should be used for keystone user creation.

[0]
https://github.com/ansible/ansible-modules-core/commit/cdf7117f7eec002ff6fce5900d2706e8a1abc399

Closes-Bug: #1526589
Change-Id: Ibe791913af52df5eb22eecdfc0f0156e2d0019a4