Fix the ouptput of docker --help should go to stdout not stderr for issue 8766
Docker-DCO-1.1-Signed-off-by: Chao Chen <chenchao@qiyi.com> (github: cc272309126)
Merge branch 'master' of github.com:cc272309126/docker
Merge branch 'master' of github.com:cc272309126/docker

Conflicts:
	pkg/mflag/flag.go
Fix the output of docker --help should go to stdout not stderr for issue 8814