This cleans up attach a little bit, and moves it out of the container
package.
Really `AttachStream` is a method on `*stream.Config`, so moved if from
a package level function to one bound to `Config`.
In addition, uses a config struct rather than passing around tons and
tons of arguments.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
`StreamConfig` carries with it a dep on libcontainerd, which is used by
other projects, but libcontainerd doesn't compile on all platforms, so
move it to `github.com/docker/docker/container/stream`
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
