TMDM-7434: fixes related to LocalUser cache

- add cache update logic in Configuration.java so 'cluster' and 'model' properties reflected in LocalUser downstream in WelcomePortalAction.java
- fix wrong condition for initializing map entry for 'cluster' & 'model'
- filter out non-portal config properties returned in WelcomePortalAction

(To do: needs more thorough testing and maybe minor code update on config saves triggered from portlets)