add gnome-session-flashback

Dockerfile

@@ -63,7 +63,7 @@ RUN chmod 440 /etc/sudoers && \
     echo "LANGUAGE=${LANGUAGE}" >> /etc/environment && \
     echo "LC_ALL=${LC_ALL}" >> /etc/environment && \
     sed -i '2i export LANG=${LANG}\nexport LANGUAGE=${LANGUAGE}\nexport LC_ALL=${LC_ALL}\nexport XDG_SESSION_TYPE=x11\nexport GDK_BACKEND=x11\nexport LIBGL_ALWAYS_SOFTWARE=1\nexport GALLIUM_DRIVER=llvmpipe' /etc/xrdp/startwm.sh && \
-    echo "exec dbus-run-session -- gnome-session" >> /etc/xrdp/startwm.sh && \
+    echo "exec dbus-run-session -- gnome-session --session=gnome-flashback-metacity" >> /etc/xrdp/startwm.sh && \
     chmod +x /etc/xrdp/startwm.sh
 
 EXPOSE 3389