Rather than conflict with the unexposed task model, change the names of
the object-oriented task display to `docker <object> ps`. The command
works identically to `docker service tasks`. This change is superficial.
This provides a more sensical docker experience while not trampling on
the task model that may be introduced as a top-level command at a later
date.
The following is an example of the display using `docker service ps`
with a service named `condescending_cori`:
```
$ docker service ps condescending_cori
ID NAME SERVICE IMAGE LAST STATE DESIRED STATE NODE
e2cd9vqb62qjk38lw65uoffd2 condescending_cori.1 condescending_cori alpine Running 13 minutes ago Running 6c6d232a5d0e
```
The following shows the output for the node on which the command is
running:
```console
$ docker node ps self
ID NAME SERVICE IMAGE LAST STATE DESIRED STATE NODE
b1tpbi43k1ibevg2e94bmqo0s mad_kalam.1 mad_kalam apline Accepted 2 seconds ago Accepted 6c6d232a5d0e
e2cd9vqb62qjk38lw65uoffd2 condescending_cori.1 condescending_cori alpine Running 12 minutes ago Running 6c6d232a5d0e
4x609m5o0qyn0kgpzvf0ad8x5 furious_davinci.1 furious_davinci redis Running 32 minutes ago Running 6c6d232a5d0e
```
Signed-off-by: Stephen J Day <stephen.day@docker.com>
