This fix tries to improve the display of `docker service ls`
and adds `--format` flag to `docker service ls`.
In addition to `--format` flag, several other improvement:
1. Updates `docker stacks service`.
2. Adds `servicesFormat` to config file.
Related docs has been updated.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>
Yong Tang