nsenter: properly unlock thread in error paths
nsenter: properly unlock thread in error paths

dm0-/mantle,mischief/mantle,mischief/mantle,quantum/coreos-mantle,dm0-/mantle,glevand/coreos--mantle,marineam/mantle,marineam/mantle,mjg59/mantle,mjg59/mantle,quantum/coreos-mantle,glevand/coreos--mantle