lxc-start-ephemeral: Use argparse errors
lxc-start-ephemeral: Use argparse errors

Use argparse's error function instead of our own print + exit.

Signed-off-by: Stéphane Graber <089afc6d81f66f1168a9849e15660feae286e024@ubuntu.com>
Acked-by: Serge E. Hallyn <3df611b026e4639bee8aef7a4beb2e39fcebb313@ubuntu.com>

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