--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)
Upstream-commit: 61b129d81802e3c988cc0e67e488b24968dd748a
Component: engine

components/engine/docker/flags.go

@@ -26,6 +26,7 @@ var (
 	flEnableCors  = flag.Bool([]string{"#api-enable-cors", "-api-enable-cors"}, false, "Enable CORS headers in the remote API")
 	flTls         = flag.Bool([]string{"-tls"}, false, "Use TLS; implied by tls-verify flags")
 	flTlsVerify   = flag.Bool([]string{"-tlsverify"}, false, "Use TLS and verify the remote (daemon: verify client, client: verify daemon)")
+	flHelp        = flag.Bool([]string{"h", "-help"}, false, "Print usage")
 
 	// these are initialized in init() below since their default values depend on dockerCertPath which isn't fully initialized until init() runs
 	flCa    *string