Review Request 69105: Added 'task atach' subcommand to new CLI.

[Armand Grillet]

-----------------------------------------------------------
This is an automatically generated e-mail. To reply, visit:
https://reviews.apache.org/r/69105/
-----------------------------------------------------------

Review request for mesos and Kevin Klues.


Bugs: MESOS-6551
    https://issues.apache.org/jira/browse/MESOS-6551


Repository: mesos


Description
-------

Added 'task atach' subcommand to new CLI.


Diffs
-----

  src/python/cli_new/lib/cli/plugins/task/main.py 
546ad00ee88fa51c54520a94da19752d010004a8 


Diff: https://reviews.apache.org/r/69105/diff/1/


Testing
-------

```
$ sudo bin/mesos-master.sh \
    --ip=127.0.0.1 \
    --work_dir=/var/lib/mesos


$ sudo bin/mesos-agent.sh 
    --master=127.0.0.1:5050 \
    --work_dir=/var/lib/mesos \
    --image_providers=docker \
    --executor_environment_variables="{}" \
    --isolation="cgroups/all,filesystem/linux,docker/runtime,namespaces/pid"    


$ sudo src/mesos-execute \
    --master=127.0.0.1:5050 \
    --name=tty-test \
    --docker_image=library/alpine \
    --no-shell \
    --tty \
    --command="sh -i"
$ cd src/python/cli_new
$ source activate
$ mesos task attach tty-test
sh-4.3$
```


Thanks,

Armand Grillet