Add Packages.vnc_packages to fix bnc#895070 and bnc#896178

Is what the old code in ```modePackages``` (used during installation) did
```
packages.concat [ "yast2-qt", "xorg-x11-Xvnc", "xorg-x11-fonts", "icewm", "sax2-tools", "yast2-x11", "xinetd" ]
```
As opposed to the code in Remote.Write (used in a running system):
```
packages = ["xinetd", "xorg-x11", PKG_CONTAINING_FW_SERVICES]
```
I wanted to keep the behavior.