[WFLY-490] / [WFLY-2270] Add an integrity check during the MODEL stage to verify that a duplicate scoped role does not already exist.

Internally host and server group scoped roles must be unique ignoring case.
Also add a check that the scoped role name does not match the standard role name.
[WFLY-490] / [WFLY-2270] Enhance the base-role attribute definition so that it is validated against the current list of standard roles.

Also correct the case if the user supplied case does not match the case of the standard role.