Docker: Use id of current user to run the container

This ensures typical files created in the build process are
accessible and removable(!) by the user outside.

Downside is that some commands (e.g. whoami) won't work well
within the container as that user typically is not listed in
/etc/passwd etc. inside the container. Buildsteps requiring
them won't work until the container image is (re-)created with
this data in place.

In general, there seems to be no silver bullet for this problem.
An extensive discussion of pros and cons can be found at
https://jtreminio.com/blog/running-docker-containers-as-current-host-user

Change-Id: I0421e031324ffe3d64b9aeede289a43357c46e3d
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/docker/dockerdevice.cpp

@@ -68,6 +68,11 @@
 #include <QTextBrowser>
 #include <QThread>
 
+#ifdef Q_OS_UNIX
+#include <unistd.h>
+#include <sys/types.h>
+#endif
+
 using namespace Core;
 using namespace ProjectExplorer;
 using namespace QtSupport;
@@ -579,6 +584,10 @@ void DockerDevicePrivate::tryCreateLocalFileAccess()
                                     "-e", "XAUTHORITY=/.Xauthority",
                                     "--net", "host"}};
 
+#ifdef Q_OS_UNIX
+    dockerRun.addArgs({"-u", QString("%1:%2").arg(getuid()).arg(getgid())});
+#endif
+
     for (const QString &mount : qAsConst(m_mounts))
         dockerRun.addArgs({"-v", mount + ':' + mount});