GUI-1226 Refresh the ARN field when the path is updated on the IAM user detail pa...

...ge
https://eucalyptus.atlassian.net/browse/GUI-1226
Boto's update_user() call doesn't seem to return the user object,

{u'update_user_response': {u'response_metadata': {u'request_id': u'da5b505b-007c-467d-8490-e7bc4d4e308b'}}}