--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)
Victor Vieux