set lxc.rootfs.backend on copy/snapshot as well
set lxc.rootfs.backend on copy/snapshot as well

Signed-off-by: Christian Brauner <48455ab3070520a2d174545c7239d6d0fabd9a83@mailbox.org>

federicobriata/lxc,thmo/lxc,GreatFruitOmsk/lxc,aeris/lxc,ysbnim/lxc,GreatFruitOmsk/lxc,hallyn/lxc,ss1h2a3tw/lxc,terceiro/lxc,QingweiPeterLan/cs188-lxc,caglar10ur/lxc,thmo/lxc,hallyn/lxc,QingweiPeterLan/cs188-lxc,aeris/lxc,ss1h2a3tw/lxc,caglar10ur/lxc,cjwatson/lxc,hfuCN/lxc,LynxChaus/lxc,ysbnim/lxc,cjwatson/lxc,LynxChaus/lxc,ysbnim/lxc,hallyn/lxc,aeris/lxc,QingweiPeterLan/cs188-lxc,GreatFruitOmsk/lxc,akshaykarle/lxc,LynxChaus/lxc,caglar10ur/lxc,federicobriata/lxc,cjwatson/lxc,federicobriata/lxc,terceiro/lxc,akshaykarle/lxc,ss1h2a3tw/lxc,thmo/lxc,akshaykarle/lxc,hfuCN/lxc,hfuCN/lxc,terceiro/lxc