cache whether 'optional' was in mntopts
cache whether 'optional' was in mntopts

after commit 4e4ca16158f91ac1271495638a4e62881169474e we are
checking for optional in mntopts after we forcibly remove it.
Cache whether we had it before removing it.

Signed-off-by: Serge Hallyn <3df611b026e4639bee8aef7a4beb2e39fcebb313@ubuntu.com>

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