Fix problem with = in completion of docker global options
Fix problem with = in completion of docker global options

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 <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@albersweb.de>

e11137/cli,riyazdf/cli,redpanda/cli,e11137/cli,thaJeztah/cli,ashfall/cli,Zebrilee/cli,Zebrilee/cli,allencloud/cli,docker/cli,thaJeztah/cli,dnephin/cli,allencloud/cli,redpanda/cli,cpuguy83/cli,ashfall/cli,riyazdf/cli,dnephin/cli,docker/cli,cpuguy83/cli