Only set the terminal in raw mode for commands which need it

Only set the terminal in raw mode for commands which need it

The raw mode is actually only needed when you attach to a container.
Having it enabled all the time can be a pain, e.g: if docker crashes
your terminal will end up in a broken state.

Since we are currently missing a real API for the docker daemon to
negotiate this kind of options, this changeset actually enable the raw
mode on the login (because it outputs a password), run and attach
commands.

This "optional raw mode" is implemented by passing a more complicated
interface than io.Writer as the stdout argument of each command. This
interface (DockerConn) exposes a method which allows the command to set
the terminal in raw mode or not.

Finally, the code added by this changeset will be deprecated by a real
API for the docker daemon.