Description of problem:
The docker help command does not print to stdout, instead it prints to stderr.  This goes against pretty much every other command that has a help function.

Version-Release number of selected component (if applicable):
Client version: 0.11.1
Client API version: 1.11
Go version (client): go1.2.1
Git commit (client): fb99f99/0.11.1
Server version: 0.11.1
Server API version: 1.11
Git commit (server): fb99f99/0.11.1
Go version (server): go1.2.1

How reproducible:
always

Steps to Reproduce:
1. run "docker help"
or
1. run "docker help <command>"
or
1. run "docker --help"
or
1. run "docker <command> --help"
or
1. run a command incorrectly, ex: "docker attach"

Actual results:
Using my favorite program that reads from stdout, grep, you can illustrate the problem here:

------------------------------------
 ❯ docker help attach | grep proxy

Usage: docker attach [OPTIONS] CONTAINER

Attach to a running container

  --no-stdin=false    Do not attach stdin
  --sig-proxy=true    Proxify all received signal to the process (even in non-tty mode)
------------------------------------

the only way this works is by doing:

------------------------------------
 ❯ docker help attach 2>&1 | grep proxy
  --sig-proxy=true    Proxify all received signal to the process (even in non-tty mode)
------------------------------------

Typically usage statements are not considered things that should be printed to errors, only error messages are considered errors.

------------------------------------
 ❯ docker attach
                                   <<<<<< no error message to stderr
                                   -------usage below should be stdout
Usage: docker attach [OPTIONS] CONTAINER

Attach to a running container

  --no-stdin=false: Do not attach stdin
  --sig-proxy=true: Proxify all received signal to the process (even in non-tty mode)
------------------------------------




Expected results:
Usage statements would be printed to stdout always so things like this would work:

------------------------------------
 ❯ docker help attach | grep proxy
  --sig-proxy=true    Proxify all received signal to the process (even in non-tty mode)
------------------------------------

In addition, misuse of commands should print out an error to stderr, and [optionally] the usage to stdout:

------------------------------------
 ❯ docker attach
Error: attach requires a container   <<<< printed to stderr
Usage: docker attach [OPTIONS] CONTAINER   <<< printed to stdout

Attach to a running container

  --no-stdin=false    Do not attach stdin
  --sig-proxy=true    Proxify all received signal to the process (even in non-tty mode)


Additional info:
Needed
 - Help and usage statements printed to stdout
 - Error messages for incorrect invocations of commands printed to stderr
This applies to all docker subcommands.