Summary: Admin Console: change admin user text field to label
Description: Username value is a text field. By default, it is "admin" and
it is the uid attribute value of admin entry. It can be changed (e.g.,
newadmin), but the uid attribute value is not touched. This causes both
"newadmin" and "admin" can be used to login, which is confusing. Since uid
attribute value is not modified together, there is no much sense to allow
the username modifiable. changing the type to label.