OHAI-416: rescue if xenstore-ls does not exist
OHAI-416: rescue if xenstore-ls does not exist

Just in case.

jbfavre/ohai,cmluciano/ohai,MSOpenTech/ohai,jaymzh/ohai,higanworks/ohai,shtzr840329/ohai,numericillustration/ohai,acaiafa/ohai,juliandunn/ohai,dreamnite/ohai,johnbellone/ohai,shtzr840329/ohai,btm/ohai,juliandunn/ohai,broadinstitute/ohai,nathwill/ohai,criteo-forks/ohai,http-418/ohai,n-marton/ohai,adamleff/ohai,nathwill/ohai,MSOpenTech/ohai,jseely/ohai,zuazo-forks/ohai,mattray/ohai,bougyman/ohai,sh9189/ohai,Juniper/ohai,chef/ohai,higanworks/ohai,jbfavre/ohai,btm/ohai,bougyman/ohai,davide125/ohai,glennmatthews/ohai,zshuo/ohai,davide125/ohai,jseely/ohai,http-418/ohai,Fodoj/ohai,glennmatthews/ohai,phreakocious/ohai,dreamnite/ohai,broadinstitute/ohai,375gnu/ohai,zshuo/ohai,sh9189/ohai,johnbellone/ohai,mattray/ohai,adamleff/ohai,n-marton/ohai,cmluciano/ohai,jaymzh/ohai,Fodoj/ohai,375gnu/ohai,tas50/ohai-1,Juniper/ohai,tas50/ohai-1,acaiafa/ohai,numericillustration/ohai,phreakocious/ohai,criteo-forks/ohai,chef/ohai