Docker: Do not use hard-coded /tmp

Amends 8c7b6a7549.

Change-Id: Ie702c7ccc5ac897920f1b8eda00dd90378a2d80b
Reviewed-by: hjk <hjk@qt.io>

src/plugins/docker/dockerdevice.cpp

@@ -1118,7 +1118,7 @@ int DockerDevicePrivate::runSynchronously(const CommandLine &cmd) const
 
     QtcProcess proc;
     proc.setCommand(dcmd);
-    proc.setWorkingDirectory("/tmp");
+    proc.setWorkingDirectory(QDir::tempPath());
     proc.start();
     proc.waitForFinished();