Container.exec_run returns None as exit_code if stream or socket
Container.exec_run returns None as exit_code if stream or socket

Signed-off-by: Frank Sachsenheim <72aca1c49f1c98da99c7c6d3471c46b3b9f9e43e@riseup.net>

docker/docker-py,vdemeester/docker-py,youhong316/docker-py,funkyfuture/docker-py,funkyfuture/docker-py,vdemeester/docker-py,youhong316/docker-py,docker/docker-py