show additional info if btrfs subvolume deletion fails (issue #315)
show additional info if btrfs subvolume deletion fails (issue #315)

Unprivileged users require "-o user_subvol_rm_allowed" mount option for btrfs.
Make the INFO level message to ERROR to make it clear, which now says following;

[caglar@qop:~] lxc-destroy -n rubik
lxc_container: Is the rootfs mounted with -o user_subvol_rm_allowed?
lxc_container: Error destroying rootfs for rubik
Destroying rubik failed

Signed-off-by: S.Çağlar Onur <acf5ae661bb0a9f738c88a741b1d35ac69ab5408@10ur.org>
Acked-by: Serge E. Hallyn <3df611b026e4639bee8aef7a4beb2e39fcebb313@ubuntu.com>

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