lxc-download: improve help text.
lxc-download: improve help text.

--help and --list are special in the sense that they
are independent of the other options and exit early.
Document them separately.

Signed-off-by: Michael Adam <dcf2bf3ff8ea93047d51252815aac9756207ea09@samba.org>
Acked-by: Stéphane Graber <089afc6d81f66f1168a9849e15660feae286e024@ubuntu.com>

cjwatson/lxc,christiaan/lxc,lazy404/lxc,virajs/lxc,yubo/lxc,bostjan/lxc,federicobriata/lxc,lazy404/lxc,hfuCN/lxc,codebauss/lxc,jirislaby/lxc,federicobriata/lxc,rldleblanc/lxc,ysbnim/lxc,armcc/lxc,christiaan/lxc,thmo/lxc,hkjolhede/lxc,lisongmin/lxc,fwilson42/lxc,regit/lxc,caglar10ur/lxc,ioops/lxc,QingweiPeterLan/cs188-lxc,LynxChaus/lxc,ioops/lxc,hallyn/lxc,ksperis/lxc,efiop/lxc,cjwatson/lxc,ss1h2a3tw/lxc,bmoar/lxc,yubo/lxc,DarknessBeforeDawn/lxc,lisongmin/lxc,tych0/lxc,jirislaby/lxc,QingweiPeterLan/cs188-lxc,Pelagicore/lxc,fwilson42/lxc,Ponce/lxc,Pelagicore/lxc,raspberrypython/lxc,major/lxc,efiop/lxc,bostjan/lxc,tych0/lxc,virajs/lxc,Distrotech/lxc,Ponce/lxc,akshaykarle/lxc,fwilson42/lxc,rldleblanc/lxc,ss1h2a3tw/lxc,bostjan/lxc,szaszg/lxc,DarknessBeforeDawn/lxc,hallyn/lxc,rowhit/lxc,ecarrara/lxc,sapun/lxc,raspberrypython/lxc,JohnPeacockMessageSystems/lxc,christiaan/lxc,aeris/lxc,hallyn/lxc,ecarrara/lxc,terceiro/lxc,ksperis/lxc,LynxChaus/lxc,jirislaby/lxc,thmo/lxc,yubo/lxc,Distrotech/lxc,ysbnim/lxc,federicobriata/lxc,hkjolhede/lxc,hfuCN/lxc,terceiro/lxc,akshaykarle/lxc,bmoar/lxc,Distrotech/lxc,codebauss/lxc,Pelagicore/lxc,LynxChaus/lxc,QingweiPeterLan/cs188-lxc,GreatFruitOmsk/lxc,DarknessBeforeDawn/lxc,terceiro/lxc,thmo/lxc,aeris/lxc,regit/lxc,major/lxc,caglar10ur/lxc,ksperis/lxc,raspberrypython/lxc,aeris/lxc,szaszg/lxc,hfuCN/lxc,ysbnim/lxc,rowhit/lxc,rldleblanc/lxc,ecarrara/lxc,efiop/lxc,lazy404/lxc,virajs/lxc,codebauss/lxc,JohnPeacockMessageSystems/lxc,major/lxc,armcc/lxc,rowhit/lxc,JohnPeacockMessageSystems/lxc,regit/lxc,szaszg/lxc,akshaykarle/lxc,armcc/lxc,Ponce/lxc,cjwatson/lxc,ioops/lxc,hkjolhede/lxc,lisongmin/lxc,tych0/lxc,sapun/lxc,GreatFruitOmsk/lxc,GreatFruitOmsk/lxc,bmoar/lxc,sapun/lxc,ss1h2a3tw/lxc,caglar10ur/lxc