[MSI] setup should not list read-only VBox-share as install-targets

A continuation of CORE-14432

I thought about how to further stress the patch that we just committed into 0.4.15-dev-2651-g864e20b

So I abused a VBox-share mounted as "read-only" and looked how ros and 2k3sp2 did behave:

Expected result
2K3_SP2_does_hide_readonly_VBoxSharedFolders.png

Observed result
but ros does erroneously show such a read-only VBox-share:
ros_erroneously_shows_driveG.png

So I thought: Hey, that's the proof that we just have to combine both conditions, the one from Wine with the one from DougLyons, and I tried the following patch
falseHope.patch

Unfortunately ros with that patch did still show the VBox share:
unfortunately_doesNotWork.png