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