Powerstrip is buggy in stdin mode over SSH

[lukemarsden]

When -i is passed to docker run when running over SSH in interactive mode, powerstrip doesn't terminate until some data is sent.

The following test demonstrates this:

$ ssh localhost DOCKER_HOST=unix:///var/run/docker.sock docker run ubuntu echo hello
hello
<hangs; hit enter and it goes back to the prompt>
$ ssh localhost DOCKER_HOST=unix:///var/run/docker.real.sock docker run ubuntu echo hello
hello
$ <returns to prompt immediately>