Actually create the outputmanagement interface

Summary: It's instantiated, but never created. This means that libkscreen's wayland backend is going to hang initializing.

Test Plan: Ran libkscreen against it, works with and doesn't work without patch.

Reviewers: graesslin, #plasma

Reviewed By: graesslin, #plasma

Subscribers: plasma-devel

Projects: #plasma

Differential Revision: https://phabricator.kde.org/D1524

wayland_server.cpp

@@ -244,6 +244,7 @@ void WaylandServer::init(const QByteArray &socketName, InitalizationFlags flags)
             this, [this](KWayland::Server::OutputConfigurationInterface *config) {
                 kwinApp()->platform()->configurationChangeRequested(config);
     });
+    m_outputManagement->create();
 
     m_display->createSubCompositor(m_display)->create();
 }