Update to work with libcontainer
Update to work with libcontainer

Makes pipework work with the new docker native exec driver (libcontainer).

hustcat/pipework,JamesGuthrie/pipework,ONode/pipework,abn/pipework,Rakurai/pipework,wrenth04/pipework,Altiscale/pipework,bing6/pipework,OnePaaS/pipework,palfrey/pipework,mej/pipework,osrg/pipework,mrvicadai/pipework,YujiOshima/pipework,mirzawaqasahmed/pipework,indykish/pipework,zhouqingyu/pipework,hayderimran7/pipework,snowygoose/pipework,spheresh/pipework,awanke/pipework,midonet/pipework,PeerXu/pipework,pierrecdn/pipework,haggaie/pipework,helloIAmPau/pipework,jpetazzo/pipework,ksmaheshkumar/pipework,SivagnanamCiena/pipework,deitch/pipework,sharry007/pipework