--help option and help command should print to stdout not stderr

--help and help are successful commands so output should not go to error.

    QE teams have requested this change, also users doing docker help | less
    or docker run --help | less would expect this to work.

    Usage statement should only be printed when the user asks for it.
    Errors should print error message and then suggest the docker COMMAND --help
    command to see usage information.

    The current behaviour causes the user to have to search for the error message
    and sometimes scrolls right off the screen.  For example a error on a
    "docker run" command is very difficult to diagnose.

    Finally erros should always exit with a non 0 exit code, if the user
    makes a CLI error.

Docker-DCO-1.1-Signed-off-by: Dan Walsh <dwalsh@redhat.com> (github: rhatdan)

docs/sources/reference/commandline/cli.md

@@ -15,6 +15,19 @@ or execute `docker help`:
 
       ...
 
+## Help
+To list the help on any command just execute the command, followed by the `--help` option.
+
+    $ sudo docker run --help
+
+    Usage: docker run [OPTIONS] IMAGE [COMMAND] [ARG...]
+
+    Run a command in a new container
+
+      -a, --attach=[]            Attach to STDIN, STDOUT or STDERR.
+      -c, --cpu-shares=0         CPU shares (relative weight)
+    ...
+
 ## Option types
 
 Single character commandline options can be combined, so rather than