Description of problem:
engine-setup sets 'admin' as username in the default registered provider, this results in engine SSO error when trying to use AuthorizationByUserName authorization role to authenticate.

Error message:
"Unauthorized: Error during SSO authentication access_denied : Cannot authenticate user 'admin@N/A': No valid profile found in credentials.."

Version-Release number of selected component (if applicable):
oVirt Engine Version: 4.2.0-0.0.master.20170514192031.gitbcb4208.el7.centos

How reproducible:
100%

Steps to Reproduce:
1. Install OVN using engine-setup.
2. Edit the default provider and look for the username input field.

Actual results:
'admin' is populated.

Expected results:
'admin@internal' should be populated.

Additional info:
provider log:
017-05-16 10:00:07,256   Starting new HTTPS connection (1): network-ge-1.scl.lab.tlv.redhat.com
2017-05-16 10:00:07,420   "POST /ovirt-engine/sso/oauth/token HTTP/1.1" 200 121
2017-05-16 10:00:07,423   Error during SSO authentication access_denied : Cannot authenticate user 'admin@N/A': No valid profile found in credentials..
Traceback (most recent call last):
  File "/usr/share/ovirt-provider-ovn/handlers/base_handler.py", line 99, in _handle_request
    response = self.handle_request(method, key, id, content)
  File "/usr/share/ovirt-provider-ovn/handlers/selecting_handler.py", line 52, in handle_request
    self._get_response_handler(method, key), content, id)
  File "/usr/share/ovirt-provider-ovn/handlers/keystone.py", line 30, in call_response_handler
    return json.dumps(response_handler(json.loads(content), id))
  File "/usr/share/ovirt-provider-ovn/handlers/keystone_responses.py", line 40, in post_tokens
    user_password=user_password)
  File "/usr/share/ovirt-provider-ovn/auth/plugin_facade.py", line 26, in create_token
    return auth.core.plugin.create_token(user_at_domain, user_password)
  File "/usr/share/ovirt-provider-ovn/auth/plugins/ovirt/plugin.py", line 55, in create_token
    timeout=self._timeout())
  File "/usr/share/ovirt-provider-ovn/auth/plugins/ovirt/sso.py", line 60, in create_token
    username, password, engine_url, ca_file, timeout)
  File "/usr/share/ovirt-provider-ovn/auth/plugins/ovirt/sso.py", line 53, in wrapper
    _check_for_error(result)
  File "/usr/share/ovirt-provider-ovn/auth/plugins/ovirt/sso.py", line 160, in _check_for_error
    response['error_code'], response['error']))
Unauthorized: Error during SSO authentication access_denied : Cannot authenticate user 'admin@N/A': No valid profile found in credentials..