Disable unmount option for / or /home
This disables the 'Unmount' context menu in the Places panel for discs
corresponding to / and /home.
It does not make much sense to offer an option that will always fail.
Twin of D15989 for Dolphin
Reviewers: Frameworks, ngraham
Reviewed By: ngraham
Subscribers: dfaure, broulik, ngraham, kde-frameworks-devel
Differential Revision: https://phabricator.kde.org/D16141