Bug 443416

SUMMARY
During deployment of Qt gui and opengl modules, deployment of "xcb-gl" fails because directory /home/$USER/CraftRoot/plugins/xcbglintegrations// doesn't exist. This results in AppImages lacking the ability to access OpenGL, which results in lower QML performance, due to lack of graphics acceleration.

STEPS TO REPRODUCE
1. Create a Blueprint for a graphics intensive project
2. Have "dev-utils/linuxdeploy" and "dev-utils/appimagetool" specified in blueprints as build dependencies for Linux.
>    def setDependencies(self):
>        self.buildDependencies["dev-utils/linuxdeploy"] = None
>        self.buildDependencies["dev-utils/appimagetool"] = None
>        # ...
3. On a Linux system, run blueprint: `craft project-name`
4. Then package the project as AppImage: `craft --package project-name`.
5. Test AppImage performance against non-containerized build of project.

OBSERVED RESULT
Graphics intensive project AppImage will result in high CPU consumption and frame drops during large animations of many seconds.

Packaging process will output:
>[qt/stdout] -- Deploying module: gui -- 
> [...]
>[qt/stdout] Deploying xcb-gl integrations 
>[qt/stdout] Directory /home/$USER/CraftRoot/plugins/xcbglintegrations// doesn't exist, skipping deployment
>[qt/stdout] 

>[qt/stdout] -- Deploying module: opengl -- 
>[qt/stdout] Deploying xcb-gl integrations 
>[qt/stdout] Directory /home/$USER/CraftRoot/plugins/xcbglintegrations// >doesn't exist, skipping deployment 
>[qt/stdout] 

EXPECTED RESULT
Qt gui and opengl modules deploy correctly. Resulting AppImage has performance equivalent to its non-containerized counterparts.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: KDE neon Testing Edition (host)
KDE Plasma Version: 5.22.90 (host)
KDE Frameworks Version: 5.87.0 (host) 5.86.0 (craft)
Qt Version: 5.15.3 (host) 5.15.2 and kde-qt-5 (craft)