Enable password setup in Remote administration module (VNC)

First from patches for bnc#808490.

Short story:
Enables password management for VNC sessions and solves one of issues hidden in bnc#808490. User can configure running VNC sessions with or without password protection.

A bit longer story:
Currently if you enable remote administration using YaST module no password setup is done. Xvnc is run with default settings (vncauth == ask password) and is started via xinetd. However, no password setup is done and user has to do it "manually". It requires running vncpasswd utility for creating passwd file and option setup for xinetd (manually or via another YaST module). Similarly if you want to enable vnc sessions without password protection. you need to tell it to Xvnc via editing xinetd config too.