Without this fix, `docker --log-driver fluentd --log-opt fluentd-tag=b` would complete `b` to `build`. Completion of the commands has to be nailed to __docker_pos_first_nonflag Signed-off-by: Harald Albers <github@albersweb.de> Upstream-commit: 6de8dd1a6e37ea6ef04d779c6348452c1a3c2370 Component: engine