E.g. "docker foobar run" would have printed "Command not found:
foobar" and printed the help text for "run". It should instead
print the root help message for docker.
Signed-off-by: Ben Firshman <ben@firshman.co.uk>
Upstream-commit: ef004ec03fe5aad33da7d53f196f16382c750d07
Component: engine