Description of problem:

Utf-8 encoded input is not accepted for login, fistname, lastname when creating a user, for example:

DEBUG nailgun.client:client.py:109 Making HTTP POST request to https://<hostname>:443/api/v2/users with options {'auth': None, 'verify': None, 'headers': {'content-type': 'application/json'}}, no params and data {"user": {"login": "\ud81a\udea2\u8764\u744a\u3b68\ud81d\udf82\u8e35", "password": "", "mail": "pRzHmGES@test.biz", "auth_source_id": 4}}.
WARNING nailgun.client:client.py:131 Received HTTP 422 response: {
"error": {"id":null,"errors":

,"full_messages":["Username is invalid"]}
}

Version-Release number of selected component (if applicable):
6.13 snap 10, but occurs also on 6.12 and 6.11

How reproducible:
always

Steps to Reproduce:
Try to create a user with utf-8 username either trough UI, API, or cli

Actual results:

Expected results:
Given there is a bunch of robottelo tests covering utf-8 usernames, I assume it used to work some time in the past and it is meant to be supported as a valid input. So it should be fixed or explicitly stated as no longer supported.

Additional info: