plasma-desktop containments desktop isFolder check

[Leslie Zhai]

Hi KDE developers,

For better KDE and robust MultiScreen, here comes Heavy testcase for 
Plasma MultiScreen 
https://blog.martin-graesslin.com/blog/2016/07/multi-screen-woes-in-plasma-5-7/#comment-71362

There is a tiny issue - Primary screen randomly switch to DesktopView, 
extended is not DesktopView by default
And I checked the isFolder 
https://github.com/KDE/plasma-desktop/blob/master/containments/desktop/package/contents/ui/main.qml#L50
When plugin/plugout outputs, the isFolder might need to consider more 
condition, but not only by plasmoid.pluginName == 
"org.kde.plasma.folder", correct? ;-)
Expect result: plugin new output, the primary screen keeps FolderView, 
and the extended is DesktopView by default if not change the default 
settings.

Please someone give me some advice to point out my fault, thanks a lot!

-- 
Regards,
Leslie Zhai https://git.reviewboard.kde.org/users/lesliezhai/