The login/logout script files need to be executable. To avoid the user
wondering why their script isn't executing, warn them if the file is not
executable and offer to fix it.
CCBUG: 391609
m_xdgConfigPath.filePath(QStringLiteral("/plasma-workspace/shutdown/"))
resolves to /plasma-workspace/shutdown/
Remove the leading slash to make it work properly
Taken from commit 4ce9a4a915511acbd41450da486d8e5d5bae10da in plasma-desktop
The commit history of the KCM can be followed in 9db1c0593e84cdb705fc61cddbdc4e5a9c318b97