qt quick项目offscreen模式下崩溃的问题处理

在基于squish搭建qt的冒烟工程的时候遇到一个问题,测试工程切成离屏模式运行时,包含qml功能的页面崩溃;

错误堆栈如下:
```
(QWindowSystemInterface::sendWindowSystemEvents(QFlags<QEventLoop::ProcessEventsFlag>))) [0x7fc925b3fa2b]
libqoffscreen.so(+0x14580) [0x7fc91a804580]
```

处理办法是设置qml走软渲染:

export QT_QPA_PLATFORM='offscreen'
export QMLSCENE_DEVICE='softwarecontext'

参考:
https://stackoverflow.com/questions/52527672/crash-when-running-qt-application-on-ubuntu-server
https://stackoverflow.com/questions/33090346/is-there-any-way-to-use-qtwebengine-without-opengl