log OnStart/OnStop hook errors
log OnStart/OnStop hook errors

The problem here is that liblxc doesn't log errors in hooks, it just logs
the exit code, so if a hook fails and someone isn't running in debug mode,
we really have no way to figure out what went wrong. Let's at least log the
error that the hook gave.

Signed-off-by: Tycho Andersen <10c18fcb898ee6b17d6575d444b125d10b3f4d6a@canonical.com>

chrisglass/lxd,akshaykarle/lxd,georghopp/lxd,pcdummy/lxd,techtonik/lxd,jsavikko/lxd,Skarlso/lxd,stgraber/lxd,akshaykarle/lxd,lxc/lxd,georghopp/lxd,mjeanson/lxd,Skarlso/lxd,Skarlso/lxd,pcdummy/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,georghopp/lxd,hallyn/lxd,Skarlso/lxd,hallyn/lxd,techtonik/lxd,atxwebs/lxd,stgraber/lxd,lxc/lxd,lxc/lxd,lxc/lxd,jsavikko/lxd,hallyn/lxd,chrisglass/lxd,erikmack/lxd,akshaykarle/lxd,atxwebs/lxd,hallyn/lxd,hallyn/lxd,lxc/lxd,lxc/lxd,jsavikko/lxd,stgraber/lxd,erikmack/lxd,atxwebs/lxd,erikmack/lxd,techtonik/lxd,mjeanson/lxd,atxwebs/lxd,hallyn/lxd,chrisglass/lxd,stgraber/lxd,mjeanson/lxd,pcdummy/lxd,stgraber/lxd