Global Menu Not Working for Virt-Manager on KDE Plasma.

[morettimarco]

This is a an open bug for virt-manager reported here: virt-manager/virt-manager#787
In order to work around the issue, the prefix GDK_BACKEND=x11 should be added to the command.
This should be done in the file /usr/share/applications/virt-manager.desktop
Here's a segment of the corrected file:

Icon=virt-manager
Exec=env GDK_BACKEND=x11 virt-manager
Type=Application
Terminal=false
Categories=System;Emulator;GTK;
Keywords=virtualization;lib